FOUS11 KWBC 270728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Sat Sep 27 2025

Valid 12Z Sat Sep 27 2025 - 12Z Tue Sep 30 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax






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FOUS11 KWBC 011801
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 PM EDT Wed Oct 1 2025

Valid 00Z Thu Oct 02 2025 - 00Z Sun Oct 05 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Fracasso


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FOUS11 KWBC 041812
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EDT Sat Oct 4 2025

Valid 00Z Sun Oct 05 2025 - 00Z Wed Oct 08 2025

...Northern Rockies...
Days 1-2...

Upper level progression remains steadfast from previous forecasts
with the closed upper reflection now analyzed as a vigorous open
wave taking on a negative tilt as it migrates northeast out of the
Great Basin into the adjacent northern Rockies. Consensus on heavy
snow beginning across the higher terrain of southwest MT into
northwest WY later this afternoon remains with some of the ridges
likely to have switched over in the past few hrs. as heights
continue to fall precipitously with the upper level progression. At
the surface, a strong surface reflection is analyzed over the UT/CO
border with an expected progression to the north-northeast over the
next 24 hrs. The combination of a favorable upper level
progression and strengthening axis of deformation over southern MT
and northern WY will lead to a significant heavy snow event, the
first of the season across the Absaroka/Beartooth/Wind River ranges
with the Big Horns getting into the heavy snow threat a little
later this evening as the height falls shift east. Heavy snow is
likely over these ranges overnight into early tomorrow morning
leading to rates between 1-2"/hr at times generating a swath of 6+"
totals a likelihood by the time we reach sunrise tomorrow.

Behind this first, stronger shortwave, a second shortwave will
dive south out of Alberta and into the Northern Rockies on Sunday.
The presence of this second shortwave will support maintaining
heavy snow into northern MT, especially Glacier NP. This digging
second shortwave will allow the larger longwave trough to remain in
place, even expanding and growing south and west. Similarly
important to the presence of these 2 shortwaves moving through the
flow and taking advantage of the abundant low level moisture, a
large polar surface high will effectively end the wintry threat
from north to south. This is because the polar high will also be
quite dry, so it will move the moisture feeding the snow on towards
the north and east. With that polar low in place, expect
temperatures to tumble well down into the 30s. Thus, as is very
common in the wintertime, the limited time between the advancing
cold/dry air and the retreating atmospheric moisture will favor
certain areas, such as the Beartooth Range, while keeping many
others on the Plains bone dry. With the advancing cold air, snow
levels will fall to as low as 5,000 ft, but the dryness should hold
any heavy snow occurring to Sunday morning, before the snow ends
from north to south.

WPC probabilities for 6 inches or more of snow remain elevated between
50 and 90% for the Beartooth, Absarokas, and Big Horn ranges while probabilities are a bit lower, between 60 and 80% for the Wind
River range.

The probability of significant icing is less than 10 percent.

Wegman/Kleebauer






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FOUS11 KWBC 251735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
135 PM EDT Thu Sep 25 2025

Valid 00Z Fri Sep 26 2025 - 00Z Mon Sep 29 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Weiss


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FOUS11 KWBC 281806
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Sun Sep 28 2025

Valid 00Z Mon Sep 29 2025 - 00Z Thu Oct 02 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell




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FOUS11 KWBC 010720
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Wed Oct 1 2025

Valid 12Z Wed Oct 01 2025 - 12Z Sat Oct 04 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Mullinax


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FOUS11 KWBC 250728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Thu Sep 25 2025

Valid 12Z Thu Sep 25 2025 - 12Z Sun Sep 28 2025

Note: Beginning today, WPC has officially resumed staffing the
Winter Weather Desk for the upcoming 2025-26 cold season.

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Mullinax

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FOUS11 KWBC 261821
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Fri Sep 26 2025

Valid 00Z Sat Sep 27 2025 - 00Z Tue Sep 30 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell



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FOUS11 KWBC 280728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Sun Sep 28 2025

Valid 12Z Sun Sep 28 2025 - 12Z Wed Oct 01 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax



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FOUS11 KWBC 031808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
208 PM EDT Fri Oct 3 2025

Valid 00Z Sat Oct 04 2025 - 00Z Tue Oct 07 2025

...Northern Rockies...
Days 2-3...

Dynamic longwave pattern will transpire across the western CONUS
as we move into the weekend with a deep closed upper-low over the
Great Basin pivoting northeast into the northern Rockies before
opening up into a relatively strong negatively-tilted shortwave
trough before exiting. Strong height-falls occurring over the Basin
through the northern Rockies will allow for freezing levels to
plummet over the course of Friday night into Saturday, continuing
further into early Sunday morning. Combination of falling heights
and strong upper-level ascent across the region mixing with
elevated PWATs will generate a transition from rain to snow across
portions of the Tetons over into the Absaroka/Beartooth Ranges of
MT/WY, followed by the Big Horn mountains a bit downstream. Snow
levels will tumble to around 7000ft MSL by Sunday morning across
the terrain with a reasonable precip distribution contributing to
periods of moderate to locally heavy snow within the terrain and
adjacent foothills.

As that negatively-tilted shortwave tracks into the Plains Sunday
morning, a second shortwave rounding the back of the longwave
trough will dive southeastward out of Alberta through much of
MT from Saturday night through much of the day on Sunday. This
shortwave will result in a period of heavy snow across much of
Glacier NP late Saturday night through Sunday morning. This
secondary forcing will keep the snow that began with the first
shortwave Saturday ongoing through Sunday. The snow will end from
north to south Sunday and Sunday night. WPC probabilities for more
than 6 inches of snow remain between 50-90% for the Beartooth,
Absaroka, and Big Horn Ranges.

The probability of significant icing is less than 10 percent.

Wegman/Kleebauer






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FOUS11 KWBC 290728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Mon Sep 29 2025

Valid 12Z Mon Sep 29 2025 - 12Z Thu Oct 02 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax







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FOUS11 KWBC 020626
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Thu Oct 2 2025

Valid 12Z Thu Oct 02 2025 - 12Z Sun Oct 05 2025

...Northern Rockies...
Day 3...

An upper low over the Great Basin on Friday opens into a trough and
shifts east over the Rockies late Saturday. Lee-side cyclogenesis
over western South Dakota occurs during this time enhancing flow
from Gulf-sourced moisture over the Plains through the northern
Rockies. Snow levels through Saturday are around 9000ft over the
Absarokas, Wind Rivers, and Bighorns, above which probs for >6"
snow from 12Z Saturday to 12Z Sunday are 40-80%.


The probability of significant icing is less than 10 percent.


Jackson


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FOUS11 KWBC 030808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Oct 3 2025

Valid 12Z Fri Oct 03 2025 - 12Z Mon Oct 06 2025

...Northern Rockies...
Days 2-3...

A pair of shortwaves moving across the Intermountain West will
interact with well above normal amounts of atmospheric moisture in
the area to cause the area's first winter storm of the season at
the higher elevations from Glacier NP in northern Montana south and
east through the ranges of northern and western Wyoming through
Sunday. The first shortwave begins the period Saturday morning over
Utah, and then tracks northeast towards the northern Plains by
Sunday morning. As the stronger of the two shortwaves getting first
dibs at the excess moisture across the area, expect heavier and
longer duration snow across the ranges of far southern Montana and
northwestern Wyoming, including Yellowstone and Grand Teton NPs.
Snowfall amounts of 6-12 inches are expected at the highest
elevations where the snow is most persistent.

As that first shortwave tracks into the Plains Sunday morning, the
second shortwave rounding the back of the longwave trough will dive southeastward out of Alberta through much of Montana from Saturday
night through much of the day on Sunday. This shortwave will result
in a period of heavy snow across much of Glacier NP late Saturday
night through Sunday morning. This secondary forcing will keep the
snow that began with the first shortwave Saturday ongoing through
Sunday. The snow will end from north to south Sunday and Sunday
night. WPC probabilities for more than 6 inches of snow remain over
50% for the Beartooth and Absaroka Ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 291732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
132 PM EDT Mon Sep 29 2025

Valid 00Z Tue Sep 30 2025 - 00Z Fri Oct 03 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Weiss


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FOUS11 KWBC 300748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Tue Sep 30 2025

Valid 12Z Tue Sep 30 2025 - 12Z Fri Oct 03 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax




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FOUS11 KWBC 021827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Thu Oct 2 2025

Valid 00Z Fri Oct 03 2025 - 00Z Mon Oct 06 2025

...Northern Rockies...
Day 3...

Dual shortwaves embedded within amplifying troughing across the
western CONUS will result in the first significant snowfall across
the higher terrain of the Northern Rockies beginning Saturday
night.

A closed low exiting the Great Basin will begin to fill as it
pivots northeast and shear out in the westerlies, reaching the
Northern Plains by 12Z Sunday. Immediately in its wake, a secondary
impulse, albeit of weaker intensity, will drop into the Northern
Rockies, driving additional height falls into portions of MT and
WY. This secondary impulse will be accompanied by a cold front
digging southward at the surface, leading to cooling temperatures
and additional ascent through forced upslope. Although the greatest
moisture (PWs above the 90th percentile according to NAEFS) will
shift steadily northeast away from the region, as a surface low
strengthens over the Northern Plains, at least some theta-e ridging
will pivot westward back into WY at the same time mid-level SW flow
re-ignites over the region downstream of the secondary impulse.
This will provide sufficient moisture to regenerate precipitation,
with much of this turning to snow from the Northern Rockies to the
Absarokas, and into the ranges of NW WY including the Tetons, Big
Horns, and around Yellowstone NP. As snow levels fall to as low as
7000 ft late in the period, WPC probabilities for more than 6
inches of snow climb to above 70% across this region, with locally
as much as 12 inches possible (10-30%) in the highest terrain of
the Big Horns and Absarokas.

The probability of significant icing is less than 10 percent.

Weiss





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FOUS11 KWBC 040724
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 AM EDT Sat Oct 4 2025

Valid 12Z Sat Oct 04 2025 - 12Z Tue Oct 07 2025

...Northern Rockies...
Days 1-2...

The weather pattern across the northern Rockies remains very
similar to previous runs of the guidance. The dynamic upper level
pattern will feature a deep upper level low over Utah ejecting
northeastward into the northern Plains by early Sunday morning.
Anomalous moisture to 2.5 sigma above normal will support waves of
showers and a few thunderstorms tracking northeastward as a
developing leeside low becomes the dominant surface feature through
the weekend. The leeside low will take advantage of a shortwave
trough also pushing northeastward. This will allow the surface low
to intensify as it makes its way to the Plains. Combined with
upslope enhancement, these ingredients all coming together will
lead to a prolonged period of heavy snow. The Beartooth, Absaroka,
and Big Horn Ranges will all come in with over 50% probabilites
for 6 inches or more of snow or more through Sunday. Behind this
first, stronger shortwave, a second shortwave will dive south out
of Alberta and into the Northern Rockies on Sunday. The presence of
this second shortwave will support maintaining heavy snow into
northern MT, especially Glacier NP. This digging second shortwave
will allow the larger longwave trough to remain in place, even
expanding and growing south and west. Similarly important to the
presence of these 2 shortwaves moving through the flow and taking
advantage of the abundant low level moisture, a large polar surface
high will effectively end the wintry threat from north to south.
This is because the polar high will also be quite dry, so it will
move the moisture feeding the snow on towards the north and east.
With that polar low in place, expect temperatures to tumble well
down into the 30s. Thus, as is very common in the wintertime, the
limited time between the advancing cold/dry air and the retreating
atmospheric moisture will favor certain areas, such as the
Beartooth Range, while keeping many others on the Plains bone dry.
With the advancing cold air, snow levels will fall to as low as
5,000 ft, but the dryness should hold any heavy snow occurring to
Sunday morning, before the snow ends from north to south.

WPC probabilities for 6 inches or more of snow remain between 50
and 90% for the Beartooth and Absarokas, while probabilities are a
bit lower, between 60 and 80% for the Wind River and Bighorn
ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 260722
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 AM EDT Fri Sep 26 2025

Valid 12Z Fri Sep 26 2025 - 12Z Mon Sep 29 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax





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FOUS11 KWBC 271910
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 PM EDT Sat Sep 27 2025

Valid 00Z Sun Sep 28 2025 - 00Z Wed Oct 01 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell





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FOUS11 KWBC 301820
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
220 PM EDT Tue Sep 30 2025

Valid 00Z Wed Oct 01 2025 - 00Z Sat Oct 04 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Fracasso

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FOUS11 KWBC 050704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sun Oct 5 2025

Valid 12Z Sun Oct 05 2025 - 12Z Wed Oct 08 2025

...Northern Rockies...
Day 1...

A positively-tilted upper level trough stretching from the northern
Plains to Central California is directing much smaller shortwave
troughs around its periphery. As each shortwave moves across the
area, they've been producing an area of rain and higher elevation
snow as a surface low develops in response to the movement of the
individual shortwaves. The first shortwave is moving over the
Dakotas and taking a well-developed surface low along with it. The
surface lows have been taking advantage of an anomalous plume of
moisture from the northern Rockies to the northern Plains. This
abundance of moisture has helped support areas of snow at the
highest elevations. As the low pulls away, there may be a brief
break in the steadiest precipitation into the mountains. Meanwhile,
a second trough, not as strong but still potent, is diving south
across Idaho and will slow and turn eastward across southern
Wyoming by Monday morning. Behind this shortwave a strong polar
high will dive southward, bringing with it a much colder and drier
air mass. The combination of subsidence with the high, and the dry
air will very quickly end the snow from north to south. Into the
Beartooths and Absarokas, enough moisture may hang on to keep much
lighter snow ongoing into Tuesday morning in a few isolated areas.
By Tuesday morning, the entire longwave trough will have moved
eastward, allowing strong ridging to build into the West Coast.
This feature too will act to limit the heaviest precipitation in
all areas as subsidence works to end the snow.

With the overall forecast largely unchanged, we will see the back
edge of the precipitation move southeastward out of Canada and into
Montana by Monday afternoon. While localized upslope is a
possibility, the drier air with the advancing area of surface high
pressure will quickly win out, allowing some areas to get some
sunshine this afternoon.

WPC probabilities for over 8 inches of snow are between 60 and 80
percent for the Bighorns and Wind River Ranges through Monday
morning.

The probability of significant icing is less than 10 percent.


Wegman



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FOUS11 KWBC 051821
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Sun Oct 5 2025

Valid 00Z Mon Oct 06 2025 - 00Z Thu Oct 09 2025

...Northern Rockies...
Day 1...

Broad positively tilted upper trough across the Northern Rockies
will maintain prevalence over the next 12-24 hrs with a strong
surface ridge pressing down out of Alberta in tandem with a
shortwave progressing around the trough base, currently analyzed
over the southern portion of the ID/MT border. Forecast has been
largely unchanged with the current radar/sat composite indicating a
prevailing upslope regime across the Absaroka and northern Big
Horns with an expectation for precip to ignite over the course of
the afternoon and evening as we move into the Wind River range.
This is thanks to the progression of the shortwave migrating out of
ID leading to the final chapter in the first heavy snow event of
the season for the northern Rockies. Additional accumulations of
4-8", local to 12" are anticipated across the higher terrain

8000ft MSL) with a respectable 3-6" for areas between

5500-7000ft MSL. Light snow accumulations will be forecast below
5000ft MSL, but impacts will be negligible in the grand scheme.

WPC probabilities for the remainder of the event (00-12z Monday)
still hover between 50-70% for an additional 4+" over the Wind
River Range, but a surge of drier air with the incoming surface
ridge and vacating shortwave will lead to a quick decay of snow
chances from north to south as we move through the rest of the D1.
By tomorrow morning, snow will taper off to just scattered light
snow with only smaller additional accums expected. The threat for
winter weather will be over prior to 18z.

The probability of significant icing is less than 10 percent.


Kleebauer





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FOUS11 KWBC 060600
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Mon Oct 6 2025

Valid 12Z Mon Oct 06 2025 - 12Z Thu Oct 09 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman

$$

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FOUS11 KWBC 061713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
113 PM EDT Mon Oct 6 2025

Valid 00Z Tue Oct 07 2025 - 00Z Fri Oct 10 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman/Kleebauer




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FOUS11 KWBC 070630
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 AM EDT Tue Oct 7 2025

Valid 12Z Tue Oct 07 2025 - 12Z Fri Oct 10 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman


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FOUS11 KWBC 080600
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Wed Oct 8 2025

Valid 12Z Wed Oct 08 2025 - 12Z Sat Oct 11 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman

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FOUS11 KWBC 071849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 7 2025

Valid 00Z Wed Oct 08 2025 - 00Z Sat Oct 11 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Mullinax



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FOUS11 KWBC 081914
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Wed Oct 8 2025

Valid 00Z Thu Oct 09 2025 - 00Z Sun Oct 12 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Mullinax




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FOUS11 KWBC 090719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Thu Oct 9 2025

Valid 12Z Thu Oct 09 2025 - 12Z Sun Oct 12 2025

...Northern Rockies...
Day 3...

By the end of the short range forecast period (Sunday morning) a
sharp, negatively-tilted upper trough is forecast to impact the
northern Rockies with moderate to heavy precipitation and lowering
snow levels. The upper trough configuration is expected to develop
as a closed-low currently off the coast of the Pacific Northwest
opens up and interacts with a diving shortwave out of British
Columbia. Additionally, this pattern is favorable for increasing
upper jet dynamics and is supported by model guidance depicting a
120-140kt southwesterly jet streak extending from the central
Great Basin to the central/northern Rockies. This places the
northern Rockies in the left-exit region of the upper jet and most
favorable for upper divergence and widespread moderate
precipitation. As the upper trough moves over the region Sat night
(500 mb heights estimated to be just below the 10th climatological
percentile per the 12z NAEFS) snow levels are expected to also fall
below 6,500ft across much of the northern Rockies by early Sunday
and below 5,000ft across the Pacific Northwest, where lighter
precipitation will be located.

The most impactful snowfall through this timeframe is expected to
be located across southwest Montana as moderate precipitation
overlaps with the lowering snow levels. Latest WPC probabilities
for at least 6 inches of snowfall are 20-40% across the high
terrain of southwest Montana above 8,000ft, which is still above
many of the major mountain passes. Additionally, WSSI-P values for
moderate impacts reach 30-40% in these areas primarily due to snow
load concerns.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell



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FOUS11 KWBC 091923
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Thu Oct 9 2025

Valid 00Z Fri Oct 10 2025 - 00Z Mon Oct 13 2025

...Northern Rockies...
Day 3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The EPS shows a classic
"kissing jets" setup Saturday night with the diffluent left-exit
region of a strong 120-140 kt 250mb jet over Utah and the diffluent right-entrance region of a >100kt 250mb jet over south-central
Canada both located over western Montana. ECMWF PWAT percentiles
are likely to remain above the 90th climatological percentile
through early Sunday morning with ample moisture aloft to saturate
the DGZ over the Absaroka, Lewis Range, and Tetons. There remains
plenty of uncertainty with varying solutions on the depth/phasing
of two 500mb disturbances over the Northwest. The GFS is the most
amplified of the bunch but is is more amplified compared to the
GEFS mean, while the ECMWF/UKMET/EC-AIFS are in the middle ground
compared to the more overly amplified GFS and weaker/sheared CMC
solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive for
mid-October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into Sunday night. Snowfall rates could
approach 1"/hr in the Lewis Range and around Glacier Nat'l Park
Sunday morning, which could also foster hazardous travel conditions
in nearby passes.

WPC probabilities depict moderate chances (40-60%) for snowfall >8"
in the peaks of the Lewis Range above 7,000ft (including Glacier
Nat'l Park) on south along the Absaroka/Tetons above 8,000ft
through Sunday afternoon. Lighter snowfall accumulations as low as
6,000ft in the Lewis Range/northwest Montana and 7,000ft in the
Absaroka/Tetons are expected. WPC's Probabilistic Winter Storm
Severity Index (WSSI-P) show similar moderate chances for Minor
Impacts for the event in these mountain ranges. Other mountain
ranges are likely to receive light snow totals (2-4") as far west
as the Bitterroots and as far south as the Teton and Wind River
Ranges in western Wyoming.

The probability of significant freezing rain across CONUS is less
than 10 percent.

Mullinax



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FOUS11 KWBC 100748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Oct 10 2025

Valid 12Z Fri Oct 10 2025 - 12Z Mon Oct 13 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The EPS shows a classic
"kissing jets" setup Saturday night with the diffluent left-exit
region of a strong 120-140 kt 250mb jet over Utah and the diffluent right-entrance region of a >100kt 250mb jet over south-central
Canada both located over western Montana. 18z ECMWF depicts PWAT
percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
is the most amplified of the bunch and is more amplified compared
to the GEFS mean, while the ECMWF/UKMET/EC-AIFS are in the middle
ground compared to the more overly amplified GFS and weaker/sheared
CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive for
mid-October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into Sunday night. Snowfall rates could
approach 1"/hr in the Lewis Range and around Glacier Nat'l Park
Sunday morning, which could also foster hazardous travel conditions
in nearby passes.

Additionally, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. This will allow for snow levels to remain rather low
for this time of year (around and slightly below 4,000 ft) across
the WA Cascades along with favorable upper ascent, which may lead
to some light accumulating snow for the major mountain passes.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat'l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC's Probabilistic Winter Storm Severity Index (WSSI-P)
show similar chances for Minor Impacts for the event in these
mountain ranges. Other mountain ranges are likely to receive light
snow totals (2-4") as far west as the Bitterroots and as far south
as the Teton and Wind River Ranges in western Wyoming.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell/Mullinax




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FOUS11 KWBC 101926
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Fri Oct 10 2025

Valid 00Z Sat Oct 11 2025 - 00Z Tue Oct 14 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The synoptic-scale snapshot
of this setup features a classic "kissing jets" setup aloft
Saturday night with the diffluent left-exit region of a strong
120-140 kt 250mb jet over Utah and the diffluent right-entrance
region of a >100kt 250mb jet over south-central Canada, both
located over western Montana. Guidance across the board indicate
PWAT percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
remains the most amplified of the bunch, while the ECMWF/UKMET/EC-
AIFS are in the middle ground compared to the more overly amplified
GFS and weaker/sheared CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. The antecedent air-mass both ahead of the storm
and trailing behind the system are not exceptionally cold for mid-
October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into early Monday morning. Snowfall rates
could approach 1"/hr in the Lewis Range and around Glacier Nat'l
Park Sunday morning, which could also foster hazardous travel
conditions in nearby passes.

Farther west, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. Snow levels to remain rather low for this time of year
(around and slightly below 4,000 ft) across the WA Cascades along
with favorable upper ascent, which may lead to some light
accumulating snow for the major mountain passes. Most snowfall
accumulations topping 4" are likely to be confined to elevations
above 5,000ft.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat'l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC's Winter Storm Severity Index (WSSI) shows Minor
Impacts from the Bitterroots and Idaho Panhandle on east through
much of Montana's mountain ranges and on south through northwest
Wyoming. Some localized Moderate impacts in the higher elevations,
largely impacting passes within these ranges, are possible.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell







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FOUS11 KWBC 110736
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
336 AM EDT Sat Oct 11 2025

Valid 12Z Sat Oct 11 2025 - 12Z Tue Oct 14 2025

...Northern Rockies & WA Cascades...
Days 1-2...

Forecast remains on track for heavy snow to impact the high terrain
of the northern Rockies and WA Cascades beginning late tonight/early
Sunday morning and lasting through early next week, with certain
valley locations also potentially seeing the first snowflakes of
the season. Upper dynamics responsible for this October mountain
snow include a sharp upper trough crossing the northern Great Basin
today before taking on a negative tilt over the northern High
Plains on Sunday in tandem with a favorable duel jet structure.
This places the northern Rockies in an area of enhanced upper
divergence and lift, as well as crashing snow levels to allow for
precipitation to transition from rain to snow for areas above
5,000-6,000 ft. Snow levels are forecast to drop even lower on
Sunday across northwestern MT, where cold Canadian air noses
southward due to high pressure building to the north. This will
also allow for enhanced easterly upslope flow into the Lewis Range
and Glacier Natl Park region. Snowfall rates could peak at 1-2"/hr
in this part of northwest MT Sunday morning according to WPC's
Snowband Probability Tracker and make for difficult driving
conditions, especially at some of the major mountain passes in the
region.

Meanwhile, a separate deepening upper low will rotate southward
within the broad western U.S. trough by Sunday night over western
WA and provide additional lift along with a sinking cold front into
northern WA. Here, snow levels are expected to drop below 3,500ft
across the northern Cascades and contain light to moderate
snowfall at times into early Monday. WPC probabilities for greater
than 8" through Monday morning are high (70-905) across the Lewis,
Swan, and Mission ranges of northwest MT, as well as the northern
Cascades above 6,000ft. Probabilities for at least 8" of snow are
moderate (40-70%) across southwest MT and the northern Absarokas.


...Sierra Nevada...
Day 3...

By the end of day 3 (12Z Tuesday), the aforementioned upper low is
expected to rapidly drop south along the northern/central CA coast
and orient a corridor of 500-600 kg/m/s IVT (above the 99th
climatological percentile per the 12z NAEFS) orthogonal to the
central Sierra Nevada. There does remain some uncertainty regarding
exact track of the upper low and timing of heavy precipitation,
with the GFS and UKMET remaining on the slower end. Regardless, as
the plume of moisture approaches the central Sierra on Tuesday snow
levels are expected to remain around 6,000-7,000ft and snow ratios
should remain capped at around 8-10:1 given the moist fetch off
the Pacific. WPC probabilities for at least 8" of snow in the
central Sierra are currently moderate (30-60%) above 8,000ft through
the end of day 3, with more snow potential likely into the day 4
timeframe.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell





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FOUS11 KWBC 111834
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Sat Oct 11 2025

Valid 00Z Sun Oct 12 2025 - 00Z Wed Oct 15 2025

...Northern Rockies...
Days 1-2...

A potent shortwave upper-level trough tracking through the Pacific
Northwest will generate healthy vertical ascent over the Northern
Rockies that combined with sufficient moisture aloft and falling
heights will prompt the development of moderate-to-heavy mountain
snow over the Northern Rockies starting this evening and lingering
into Sunday. As heights steadily fall and precipitation rates
increase Saturday night into Sunday morning, snow levels will drop
to as low as 4,000ft across far northwest MT but the heavier
snowfall totals (>6") will be most commonly found above 5,000ft
along the Lewis Range, including Glacier Nat'l Park. Accumulating
snowfall will extend as far west as the Blue and Sawtooth Mountains
and as far south as the Teton and Wind River Ranges of western
Wyoming through Sunday morning. Snow will stick around through
Sunday night over the Lewis Range and on the eastern foothills of
central Montana thanks to a dome of Canadian high pressure
fostering upsloping easterly flow that prolongs the heavy snowfall
into Monday morning.

WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Idaho Panhandle on east
to the Lewis Range. Mountains within and around Glacier Nat'l Park
even have moderate chances (40-60%) for over 12" of snow,
particularly above 7,000ft. Farther south into the Absaroka,
Teton, and Wind River Ranges, WPC probabilities show high chances

70%) for snowfall totals >4" above 8,000ft. Expect lighter

snowfall totals (1-4" on average, locally higher in taller peaks)
in parts of the Bitterroots, Sawtooth, and Blue Mountains. The WSSI
shows mostly Minor Impacts due to potentially slick travel
conditions, while some passes in Montana and Glacier Nat'l Park may
contend with Moderate Impacts that could result in road closures.

...Pacific Northwest & Sierra Nevada...
Days 2-3...

Farther west, as the Northern Rockies upper-level disturbance exits
north and east, another 500mb trough will strengthen and dive south
through the Pacific Northwest late Sunday and eventually deepen to
a robust 500mb low off the northern California coast by Monday
afternoon. This sudden amplification of the 500mb trough (06Z ECMWF
shows 500mb heights below the 1st climatological percentile off
the California coast Monday afternoon) is due to an impressive
anti-cyclonic weak break over British Columbia. The dramatic
height falls and modest 500-700mb CAA aloft will support lowering snow
levels along the Cascades, Olympics, and on south through the
Siskiyou and the Sierra Nevada starting Sunday and continuing into
the first half of next week. All guidance also shows a healthy IVT
topping 400 kg/m/s helping to direct plenty of Pacific moisture at
the mountain ranges. The heaviest snowfall in the Pacific Northwest
unfolds late Sunday morning and into Sunday night before gradually
tapering off by Monday morning. Monday is when snow arrives over
the northern California mountains with the heaviest snowfall
occurring Monday night into Tuesday over the Sierra Nevada.
Guidance has come in snowier over the past 12-24 hours, and given
the lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra Nevada. This could raise concerns for
potential impacts to trees and infrastructure given this is the
first significant mountain snowfall in the Sierra Nevada this
season.

WPC probabilities show minor accumulations (less than 4") as low
as 4,000ft in elevation over the Cascades and Olympics, but
elevations at and above 4,000ft sport high chances (>70%) for
snowfall totals >4" through the first half of next week. Some
peaks above 6,000ft in western OR and western WA could see
snowfall totals top 12" in spots. In California, the northern
Sierra Nevada above 7,000ft and the central Sierra Nevada above
8,000ft have moderate-to-high chances (50-80%) for >12" of
snowfall and low-to-moderate chances (30-50%) for amounts >18"
through Tuesday afternoon. Latest WSSI-P shows moderate chances
(40-60%) for Moderate Impacts along the central Sierra Nevada with
the Snow Amount, Snow Load, and Snow Rate impacts being the main
concerns for the first significant snow of the season.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax








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FOUS11 KWBC 120744
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Sun Oct 12 2025

Valid 12Z Sun Oct 12 2025 - 12Z Wed Oct 15 2025

...Northern Rockies & Pacific Northwest...
Days 1-2...

By the start of the forecast period (12Z Sunday), a potent
shortwave upper-level trough will be quickly exiting the northern
Rockies along with an associated strong surface low pushing
northeastward into southern Saskatchewan. Gradually increasing
heights are then expected across the northern Rockies through the
remainder of the day 1 forecast period, while a rapidly deepening
upper low drops southward along the coast of the Pacific Northwest.
At the surface, cold Canadian high pressure nosing southward into
northwest MT will allow for favorable upslope ascent in this
region, with general low-to-mid level convergence extending across
northern WA and ID along a sinking frontal boundary. This will
favor light to moderate snow across areas above 5,000ft, but with
snow levels dropping enough for flakes to reach into parts of the
MT Front Range and adjacent High Plains at times on Sunday night.
For the Cascades of WA and OR, snowfall will be tied to the
dropping upper low as snow levels start around 4,000-5,000ft
(lowest in the northern WA Cascades) before eventually lowering to
around 3,000ft in WA and 4,500ft in OR on day 2.

WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Cascades on eastward into
the northern Idaho Panhandle to the Lewis Range of Montana.
Mountains within and around Glacier Nat'l Park even have moderate
chances (40-60%) for over 12" of snow, particularly above 7,000ft.
The WSSI shows mostly Minor Impacts due to potentially slick travel
conditions, while some passes in Montana and Glacier Nat'l Park
may contend with Moderate Impacts that could result in road
closures.

...California...
Days 2-3...

...First heavy snowfall event of the season set to impact the
Sierra Nevada beginning Monday night...

By day 2, the upper low dropping southward along the West Coast is
forecast to deepen into a robust 500mb low off the northern
California coast. This sudden amplification of the 500mb trough
(18Z ECMWF shows 500mb heights below the 0.5 climatological
percentile and nearing October records off the California coast
Monday afternoon) is due to an impressive anti- cyclonic weak break
over British Columbia. The dramatic height falls and modest
500-700mb CAA aloft will support lowering snow levels down to
around 6000-6500ft through the Siskiyou and the Sierra Nevada
starting Monday and continuing into the first half of next week.
All guidance also shows a healthy IVT topping 400 kg/m/s helping to
direct plenty of Pacific moisture at the mountain ranges. Snow
arrives over the northern California mountains on Monday with the
heaviest snowfall occurring Monday night into Tuesday over the
Sierra Nevada. Guidance has come in snowier over the past 12-24
hours, and given the lack of deep, cold air aloft, snow is likely
to be a heavy/wet snowfall along the Sierra Nevada. This could
raise concerns for potential impacts to trees and infrastructure
given this is the first significant mountain snowfall in the Sierra
Nevada this season.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) by Wednesday morning, with maximum amounts up to 36"
possible. Latest WSSI-P shows high chances (70-99%) for Moderate
Impacts along the central Sierra Nevada with the Snow Amount, Snow
Load, and Snow Rate impacts being the main concerns for the first
significant snow of the season. Current WSSI also highlights Major
to Extreme Impacts, which would imply difficult to impossible
travel at times between Monday night and much of the day on Tuesday,
including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell/Mullinax





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FOUS11 KWBC 121913
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Sun Oct 12 2025

Valid 00Z Mon Oct 13 2025 - 00Z Thu Oct 16 2025

...Northern Rockies & Pacific Northwest...
Days 1-2...

Snow has subsided in parts of WY and central ID as the 500mb
shortwave trough responsible for snowfall late yesterday and
overnight tracks into south-central Canada. However, periods of moderate-to-heavy snow will linger over western MT as cold
Canadian high pressure nosing southward allows for favorable
upslope ascent in this region, with general low-to-mid level
convergence extending across northern WA and ID along a sinking
frontal boundary. This will favor light to moderate snow across
areas above 5,000ft, but with snow levels dropping enough for minor accumulations for parts of the MT Front Range and adjacent High
Plains above 4,000ft through tonight. For the Cascades of WA and
OR, snowfall will be tied to the amplifying upper low emerging from
British Columbia as snow levels start around 4,000-5,000ft (lowest
in the northern WA Cascades) before eventually lowering to around
3,000ft in WA and 4,500ft in OR on Monday

WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Cascades on eastward into
the northern ID Panhandle to the Lewis Range of MT. Over western
MT and the ID Panhandle, including Glacier Nat'l Park, an
additional... particularly above 7,000ft. The WSSI shows mostly
Minor Impacts, signaling potentially slick travel conditions, while
some passes in MT and Glacier Nat'l Park may contend with Moderate
Impacts that could result in road closures.

...California & Central Nevada...
Days 2-3...

...First significant snowfall event of the season set to impact
the Sierra Nevada beginning Monday night...

The upper low dropping southward along the West Coast is forecast
to deepen into a robust 500mb low off the California coast. This
amplification of the 500mb trough (06Z ECMWF shows 500mb heights
below the 0.5 climatological percentile and nearing October records
off the California coast Monday afternoon) is due to an impressive anti-cyclonic wave break over British Columbia. Height falls and
modest 500-700mb CAA aloft will support lowering snow levels down
to around 6000-6500ft through the Siskiyou and the Sierra Nevada
starting Monday and continuing through the first half of next week.
A healthy IVT topping 400 kg/m/s is helping to direct a rich plume
of Pacific moisture at the mountain ranges. Snow arrives over the
northern California mountains on Monday with the heaviest snowfall
occurring Monday night into Tuesday over the Sierra Nevada. Given
the lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra Nevada. This raises concerns for
potential impacts to trees and infrastructure given this is the
first significant mountain snowfall in the Sierra Nevada this
season. WPC's Snowband Probability Tracker shows HREF guidance
identifying 2-3"/hr rates over the central Sierra Nevada Monday
night. Look for some heavy snowfall to spill into central Nevada's
taller ranges with anywhere from 6-12" of snowfall possible.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) through Wednesday with maximum amounts exceeding 36"
possible. Latest WSSI-P shows moderate-to-high chances (50-80%)
for Major Impacts along the central Sierra Nevada with the Snow
Amount, Snow Load, and Snow Rate impacts being the main concerns
for the first significant snow of the season. Current WSSI also
highlights Moderate to Major Impacts, which would imply difficult
to impossible travel at times between Monday night and much of the
day on Tuesday, including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell






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FOUS11 KWBC 130745
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Mon Oct 13 2025

Valid 12Z Mon Oct 13 2025 - 12Z Thu Oct 16 2025

...California & Central Nevada...
Days 1-2...

...First significant snowfall event of the season set to impact
parts of the Sierra Nevada beginning Monday night...

An upper low dropping southward along the West Coast is forecast
to deepen into a robust 500mb closed low off the California coast
by Monday night before swinging inland across central California on
Tuesday and eventually the central Great Basin on Wednesday. This
rapid amplification of the 500mb closed low (18Z ECMWF shows 500mb
heights below the 0.5 climatological percentile and nearing October
records off the California coast Tuesday morning) is due to an
impressive anti- cyclonic wave break over British Columbia. Height
falls and modest 500-700mb CAA aloft will support lowering snow
levels down to around 6000-6500ft through the Siskiyou and the
Sierra Nevada starting today and continuing through early
Wednesday, with snow levels remaining around 7,000ft to start in
the southern Sierra within the more robust precipitation axis. A
healthy IVT topping 400 kg/m/s is helping to direct a rich plume of
Pacific moisture at the mountain ranges. However, recent model
trends over the last 24 hrs have indicated a slightly further south
location of the upper- low, which lowers the QPF somewhat across
the central Sierra due to less orthogonal (more southerly) flow
into the Sierra Nevada terrain. This produces better upslope flow
into the southern CA ranges (ptype primarily rain) and southern
Sierra Nevada versus the prior forecasts centered on the central
Sierra. Regardless, snow still arrives over the northern California
mountains today with the heaviest snowfall occurring late tonight
into Tuesday over the central/southern Sierra Nevada. Given the
lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra. This raises concerns for potential
impacts to trees and infrastructure given this is the first
significant mountain snowfall in the Sierra Nevada this season.
WPC's Snowband Probability Tracker shows HREF guidance identifying
2-3"/hr rates over the southern/central Sierra Nevada Monday night
into Tuesday. Look for some heavy snowfall to spill into central
Nevada's taller ranges with anywhere from 12-24" of snowfall
possible over 8,000ft.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) through Wednesday with maximum amounts up to 36"
possible. Latest WSSI-P shows moderate-to-high chances (50-80%) for
Major Impacts along the central Sierra Nevada with the Snow
Amount, Snow Load, and Snow Rate impacts being the main concerns
for the first significant snow of the season. Current WSSI also
highlights Major to Extreme Impacts, which would imply dangerous
to impossible travel at times between Monday night and much of the
day on Tuesday, including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell





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FOUS11 KWBC 131914
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Mon Oct 13 2025

Valid 00Z Tue Oct 14 2025 - 00Z Fri Oct 17 2025

...California & Central Nevada...
Days 1-2...

...First significant snowfall event of the season impacts the
Sierra Nevada tonight through Tuesday night...

A deepening low pressure system shifting south just off the far
north California coast this afternoon will swing inland across the
central California coast late tonight, cross the Sierra Nevada
Tuesday night, and north-central Nevada on Wednesday. The fairly
deep low will decrease snow levels from around 7000ft over the
Sierra Nevada tonight to as low as 5500ft Tuesday evening under the
upper low. Snow levels drop to around 6000ft over the central NV
for Tuesday night and Wednesday. A strong inland moisture surge
ahead of the low with PW around 1" will allow for moderate to heavy
snow rates above the snow level. 12Z HREF mean snow rates are
1-2"/hr over the central/southern Sierra Nevada from 06Z tonight to
15Z Tuesday.

WPC probabilities show moderate-to-high chances (40-80%) for at
least 24" of snowfall in 24hrs from 06Z tonight to 06Z Wednesday
above about 8000ft. Probabilities through that time for >8" are
30-70% around 7000ft (including Donner Pass on I-80). The WSSI
highlights Major Impacts for the High Sierra and remote central NV
ranges with moderate impacts for most cross Sierra road passes.


...North-Central Rockies...
Day 3...

The low fills as it crosses the Great Basin, but remains closed as
it crosses over WY on Thursday. Lee-side cyclogenesis forms over
southeast WY Wednesday night with an increasing easterly component
to the low level flow to aid moisture transport over the western WY
ranges through Thursday morning with snow levels around 7000ft.
However, the rates are not expected to be that great with mainly
20-30% probs for >8" snow in 24hr from 00Z Thur to 00Z Fri for the
Absarokas and Wind River Range. An exception is over the Tetons
where those probs are 40-60%.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Jackson


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FOUS11 KWBC 140729
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Tue Oct 14 2025

Valid 12Z Tue Oct 14 2025 - 12Z Fri Oct 17 2025

...California & Central Great Basin...
Days 1-2...

...First significant snowfall event of the season continues across
the Sierra Nevada today...

A deep, vertically stacked mid-upper low churning off the coast of
central CA by the start of the forecast period (12Z Tues) is
forecast to swing inland today before crossing into the central
Great Basin on Wednesday. This mid-upper low pressure system is
very anomalous for the time of year, reaching below the 0.5th
climatological percentiles and nearing October records for the
first part of day 1 just of the CA coast. The depth of the system
will allow for ample upper ascent and orographic lift throughout
the Sierra Nevada, while decreasing snow levels from around 7000ft
this morning to as low as 5500ft this evening under the upper low.
Snow levels also drop to around 6000ft over the central NV ranges
by Wednesday. The strong inland moisture surge ahead of the low and
associated with an occluded/cold front will have IVT values around
500 kg/m/s at the start of the forecast period and allow for
moderate to heavy snow rates above the snow level. 00Z HREF mean
snow rates are 1-2"/hr over the central/southern Sierra Nevada from
12Z to 18Z today, with lingering bursts of 1"/hr snow possible
over the central Sierra underneath the upper low through Tuesday
night.

WPC probabilities show moderate-to-high chances (40-80%) for at
least 12" of additional snowfall after 12Z Tuesday above about
8000ft and greatest across the southern Sierra and White/Inyo Mts
just to the east. Probabilities through that time for >8" are also
40-80% around 7000ft (including Donner Pass on I-80). The WSSI
highlights Major Impacts for the High Sierra and remote central NV
ranges with moderate impacts for most cross Sierra road passes.


...North-Central Rockies...
Days 2-3...

The low fills as it crosses the Great Basin, but remains closed as
it crosses over WY on Thursday. Lee-side cyclogenesis forms over
southeast WY Wednesday night with an increasing easterly component
to the low level flow to aid moisture transport over the western WY
ranges through Thursday morning with snow levels falling to around
7000ft after starting above 9000ft on Wednesday. Overall, snowfall rates
are not expected to be that great outside of an isolated convective
shower in the highest terrain with mainly longer duration light-to-moderate snow through the forecast period. WPC probs for >8" snow in 72hr
ending 12Z Friday are 60-90% for the Absarokas, Teton and Wind
River Range, as well as the Uinta Mts in Utah mainly above
10,000ft.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell





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FOUS11 KWBC 141902
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Tue Oct 14 2025

Valid 00Z Wed Oct 15 2025 - 00Z Sat Oct 18 2025

...Sierra through the Northern Rockies...
Days 1-3...

An impressive closed low will reach peak intensity tonight just
west of San Francisco before beginning to advect northeast on
Wednesday. NAEFS height anomalies show 500mb percentiles dropping
to below the 0.5th percentile rank in the CFSR climatology before
slowly filling as the entire longwave trough moves across the Great
Basin and then into the Rockies by Thursday. This trough is then
progged to become an open wave by Friday morning as it exits into
the Northern High Plains.

Despite the slow weakening, impressive deep layer ascent will
expand downstream of this evolution, as height falls, PVA, and a
strengthening jet streak overlap to produce surface cyclogenesis.
This low pressure will likely move steadily northeast across the
Great Basin through Wednesday night before occluding, with
secondary lee-cyclogenesis in CO likely on Thursday.

Accompanying the primary closed low tonight into Wednesday,
impressive moisture advection/IVT will push inland reflected by
moderate probabilities (>60%) for 500 kg/m/s pushing into CA and
NV. With snow levels falling beneath the upper low and behind the
cold front accompanying the surface low, this will result in heavy
snowfall, generally above 5500-6000 ft in the Sierra and into the
terrain of Nevada where WPC probabilities for 8+ inches of snowfall
are as high as 50%, with locally 12" or more possible (30%) in the
Ruby Mountains of Nevada through D1.5. Briefly heavy snowfall
rates exceeding 1"/hr are possible (30-50% chance) in the Sierra
and higher terrain of Nevada D1 thanks to elevated instability and
favorably placed ascent into the DGZ. With SLRs likely to be
modest, this will result in at least some moderate impacts at
elevated mountain passes tonight and Wednesday.

Thereafter, the intensity of the snowfall and the impacts should
decrease in response to weaker overall ascent, but heavy snow is
likely to spread into parts of UT and WY, including the Wasatch,
Uintas, and ranges around Yellowstone NP. Snow levels moderate at
this time to, generally hovering around 7000 ft, but steep lapse
rates beneath the mid-level trough could allow for some lowering to
around 6000 ft during times of heavier snowfall as theta-e lapse
rates fall to 0C/km at times suggesting convective snow shower
potential, especially during periods of pronounced upslope into
terrain features. WPC probabilities for 8+ inches on D2 are
moderate to high in the Tetons, Wind Rivers, and highest terrain
surrounding Yellowstone NP, but pass level snow should remain below
6 inches. On D3, snow wanes quickly as the system ejects to the
east, leaving just minimal additional accumulation across the
higher terrain of NW WY.

The probability of significant freezing rain across CONUS is less
than 10 percent.


Weiss


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FOUS11 KWBC 150721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Wed Oct 15 2025

Valid 12Z Wed Oct 15 2025 - 12Z Sat Oct 18 2025

...Central Great Basin & Northern Rockies...
Days 1-2...

A potent closed upper low, which impacted California and the Sierra
to start the week is forecast to cross the central Great Basin
today before lifting across the northern Rockies on Thursday. As it
does so, it is also forecast to gradually weaken, but still
provide ample broad scale upper ascent over the region. The
greatest potential for moderate to locally heavy snow will likely
be situated directly underneath the aforementioned upper low where
the greatest lift and steepest lapse rates exist. The 00z HREF
shows this potential for 1-2"/hr snowfall rates across the high
terrain throughout north-central and northeast NV between 18Z-00Z
today as snow levels drop as low as 7,000ft.

For the northern Rockies, strong south-southwesterly upslope flow
into the WY and UT mountain ranges will provide for more longevity
of moderate high elevation snowfall ahead of the mid-upper low on
Thursday. This includes the Tetons, Absarokas, Bighorns, Wind River
Range, as well as the Wasatch and Uintas of UT. Snow levels will
start out fairly high and around 9,000ft before dropping to around
7,000ft for areas underneath the mid-upper low as it pushes
northeastward. Snow should taper off by Thursday night as the
system quickly exits into the northern Plains and dry northwesterly
flow becomes the dominant regime again for the time being.

WPC probabilities for at least 8 inches of snow for this event are moderate-to-high (50-80%) across the Ruby Mts of northeast NV, as
well as many of the ranges surrounding Yellowstone NP, the WY
Bighorns, and the Uintas of UT. Most of these higher probabilities
reside over regions higher than 9,000ft in elevation.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell



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FOUS11 KWBC 151950
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Wed Oct 15 2025

Valid 00Z Thu Oct 16 2025 - 00Z Sun Oct 19 2025

...Eastern Great Basin to North-Central Rockies...
Day 1...

Low pressure over south-central Nevada this afternoon will track
northeast over UT tonight and Wyoming on Thursday. Slight weakening
is expected, but it will remain a closed low. Ongoing banding
along the deformation axis north of the low will persist over NV
and UT through tonight (where 1-2"/hr snow rates about the 7000ft
snow level are noted in the 12Z HREF over the Ruby in NV and the
Wasatch and Uinta in UT) before shifting to the WY ranges (and
northern Absarokas in southern MT) for Thursday where rates should
be more in the 0.5 to 1"/hr range above a 7500ft snow level.

Day 1 WPC PWPF (starting at 00Z tonight) for >8" snow 30-50% for
the Ruby Mts of northeast NV, Uinta of UT, the Tetons, Wind River,
Absarokas, and Bighorns in WY.


...Northern Rockies...
Day 3...

An upper trough ejects from what is currently a low over the Gulf
of Alaska and tracks down the northern Rockies of Montana and
Wyoming late Friday through Saturday morning. This reinforcing
trough will only have rather dry continental air to work with
since it is in the wake of the system crossing Wyoming from
southwest to northeast on Thursday. However, decent lift from the
trough axis should allow some moderate snow rates Friday night
through Saturday morning in terrain from around Glacier NP, eastern
Absarokas, Bighorns, and even Laramie range. Day 3 PWPF for >2"
are 20 to 50% over these ranges and closer to 70% for the Bighorns.
Snow levels dip under the upper trough passage, to around 4000ft
in northern MT, 5000ft in northern WY, and 6000ft in southern WY.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Jackson



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FOUS11 KWBC 160618
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
218 AM EDT Thu Oct 16 2025

Valid 12Z Thu Oct 16 2025 - 12Z Sun Oct 19 2025

...North-Central Rockies...
Day 1...

Upper low over southwestern Wyoming this morning will continue to
track northeastward into southeastern Montana by 00Z/17. Snow
levels will be around 7000-8000ft over the region. Light to modest
snow will continue over the Uintas and Absarokas/Wind River
Range/Bighorns this morning before ending late this afternoon into
the evening/overnight from southwest to northeast as the system
moves into the Northern Plains. WPC probabilities for at least
another 6 inches of snow after 12Z this morning are 20-50%.


...Northern Rockies...
Day 2...

Shortwave out of western Canada will slip southeastward across the
Northern Rockies Friday evening into Saturday morning, spreading
light snow across Glacier NP, southwestern
MT/Yellowstone/Absarokas, and into the Bighorns. WPC probabilities
for at least another 4 inches of snow are low (10%).

...Pacific Northwest...
Day 3...

Pacific upper low will push into southwestern Canada with a strong
130kt jet from southwest to northeast slowly sinking into the
region. Snow levels will be quite high through 00Z Sun
(6500-10,000ft across WA) but then start to crash through 12Z Sun
(end of the period) to around 5000-6000ft over the WA Cascades. WPC probabilities for at least 6 inches of snow are low (10-40%) over
the higher peaks of the Cascades through 12Z Sun.


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso

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FOUS11 KWBC 161845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
245 PM EDT Thu Oct 16 2025

Valid 00Z Fri Oct 17 2025 - 00Z Mon Oct 20 2025

...Northern/Central Rockies...
Days 1-3...

The mid-level pattern becomes increasingly progressive through the
weekend as the closed low which has brought prolonged unsettled
weather to the region fills. As this feature becomes embedded in
the more general westerlies by Friday night, it will leave pinched
W/NW flow in its wake, through which two additional disturbances
will race, producing transient periods of moderate to heavy
snowfall across the higher elevations.

On D1 /Thursday night and Friday/ some lingering mid-level moisture
will remain across the terrain of NW WY in response to a departing
surface low and increasing NW mid-level flow. While moisture is
expected to erode quickly during this period, sufficient upslope
flow into this moisture will result in periods of light to moderate
snowfall before the DGZ dries and snow ends, especially across the
Tetons and near Yellowstone NP, where WPC probabilities for an
additional 2+ inches of snow are as high as 30-50%.

After this first wave ejects to the east, a secondary shortwave
will dive southeast rapidly on its heels. This impulse is likely to
dig from southern British Columbia around 00Z/Friday to the
Central High Plains by 00Z/Saturday. A pinched vorticity streamer
accompanied by rapid sharpening of the 700mb wave will drive
intense ascent, albeit of short duration, from the Northern Rockies
through the terrain of WY. Although forcing will be quick,
favorable overlap of omega into the DGZ combined with modest 0-2km
fgen will likely result in a fluffier-than-normal snowfall with
SLRs likely above climo but with briefly intense rates above 1"/hr.
This will result in a few inches of snowfall as reflected by
WPC probabilities that reach as high as 50% for 4+ inches across
the Absarokas and Big Horns. Gusty winds will likely accompany
this wave and some low-end probabilities (10-20%) for moderate
blowing snow impacts from the WSSI-P move across the area during
this time as well, indicating a threat for convective snow bursts
or even an isolated snow squall Friday night.

Thereafter, yet another wave, the third in the series, will
approach the Pacific Northwest Coast and then dive into the
Northern Rockies by the end of the period. This system will be more
impressive with impressive height falls digging out of British
Columbia leading to robust downstream IVT surging into the region

80% chance for 250 kg/m/s reaching well into the interior West).

With the accompanying WAA, snow levels will rise steadily to
7000-8000 ft, but then crash with the accompanying cold front to
around 5000 ft by 00Z Monday. This will result in varying snow
levels with generally below climo SLR producing impacts due to snow
load as reflected by the WSSI-P, but additional snowfall before the
end of D3 is expected to be light and confined to the Northern
Rockies near Glacier NP.


...Pacific Northwest...
Day 3...

A strong upper low (500mb heights dropping below the 10th
climatological percentile according to NAEFS) will dig along the
British Columbia coast driving height falls into the Pacific
Northwest on Sunday. These height falls will be accompanied by
vorticity streamers/PVA, and increasing LFQ diffluence as a jet
streak pivots southward upstream of the primary trough axis.
Together, this will result in increasing ascent into a moistening
column thanks to IVT reaching above 500 kg/m/s (>80% chance) into
coastal WA and OR. The result of this overlap will be an expanding
area of precipitation, with snow likely becoming more widespread as
snow levels fall through the day. Initially, snow should be
confined to just the highest terrain of the Northern Cascades, but
by the end of D3 snow levels fall to around 5000 ft (NBM 10th/25th
percentiles seem reasonable due to strong ascent and steepening
lapse rates) leading to more widespread snow and at least some
impacts at the passes. WPC probabilities on Sunday at high (>70%)
for more than 4 inches in the Northern Cascades above 6000 ft and
in the higher peaks including Mt. Rainier.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Weiss


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FOUS11 KWBC 170659
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Fri Oct 17 2025

Valid 12Z Fri Oct 17 2025 - 12Z Mon Oct 20 2025

...Northern Rockies...
Day 1...

A 125kt jet along 50N into southwestern BC will dip down across
the US/Canadian border as mid-level height falls push into western
MT late this afternoon and overnight. A surface cold front will
move quickly through the region with NW flow in its wake,
supporting a broader area of light snow and some enhanced upslope-
driven snow for the MT Absarokas and into the Bighorns. WPC
probabilities of at least 4 inches of snow are about 20-60% above
8000-9000ft.

...Pacific Northwest and Northern Rockies...
Days 2-3...

A buckled upper jet will move into the Pacific Northwest early
Sunday, with a cold front and attendant atmospheric river of
moisture aimed into the region from the southwest. High snow levels
above 7000ft early Sunday (coincident with the heavier
precipitation) will lower to just under 5000ft Sunday
afternoon/evening as heights reach their lowest point in the fast
flow. Snow will quickly spread from the WA Cascades eastward to the
northern Rockies (western MT/Idaho into northwestern WY) as the
cold front races eastward. WPC probabilities for at least 8 inches
of snow days 2-3 are >50% above about 5000ft over the WA Cascades
and around 6500ft in northwestern MT.

The probability of significant freezing rain across CONUS is less
than 10 percent.


Fracasso


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FOUS11 KWBC 171859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Fri Oct 17 2025

Valid 00Z Sat Oct 18 2025 - 00Z Tue Oct 21 2025

...Northern Rockies...
Day 1...

A fast moving 500mb shortwave trough at the nose of a 130kt jet
streak will provide sufficient upper-level ascent aloft at the same
time as a cold front passes through the northern Rockies tonight.
The atmospheric column will be saturated enough to support light-
to-moderate mountain snow along the Lewis Range, the Absaroka, and
Big Horns tonight and into Saturday morning. Snow levels in the
Lewis Range will hover as low as 6,000ft while the Absaroka and Big
Horns are as low as 7,000ft. The heavier amounts in the Absaroka
and Big Horns are more likely to be observed above 8,000ft with WPC probabilities suggest low-to-moderate chances (20-50%) for snowfall
totals >4" through Saturday morning. Most of the Lewis Range will
generally see minor accumulations (coating-3") through Saturday
morning.

...Pacific Northwest and Northern Rockies...
Days 2-3...

A strong northeast Pacific low pressure system will direct its cold
front and attendant atmospheric river at the Pacific Northwest on
Saturday. The rich 850-500mb moisture field will spill over into
western WA Saturday afternoon, then into the ID Panhandle and and
northern Rockies Saturday night and into Sunday. The sternest lift
at mid-to-upper levels of the atmosphere occurs late Saturday
night and into Sunday as sharply decreasing height falls and 500mb
PVA allows to heavier snowfall rates and lowering snow levels.
While this jet stream pattern is supportive of mountain snow, the
cold air in wake of the frontal passage is not exceptionally cold.
For this reason, snow levels in the Cascades and Olympics may reach
as low as 4,000ft but most passes should be just low enough in
elevation to avoid the heavier snowfall totals that are expected
at 5,000ft and up. WPC probabilities show moderate-to-high chances
(50-80%) for snowfall >6" at elevations >5,000ft in the Cascades.
Farther east, the Bitterroots, Lewis Range, Absaroka, and Tetons
are forecast to see minor-to-moderate snowfall that lingers in
parts of western MT through Monday morning. WPC probabilities show
the Lewis Range above 6,000ft and the Absaroka above 8,000ft with
the moderate-to-high chances (40-70%) for snowfall totals >6" by
the time the event concludes Monday afternoon. Localized snowfall
totals over 12" are possible in the tallest peaks of the Lewis
Range and Absaroka.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax



$$

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FOUS11 KWBC 180655
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Sat Oct 18 2025

Valid 12Z Sat Oct 18 2025 - 12Z Tue Oct 21 2025


...Pacific Northwest and Northern Rockies...
Days 1-2...

A fairly amplified yet progressive pattern will take a strong
Pacific low pressure system into British Columbia tonight in a
weakening state. Its attendant cold front will promote a modest
atmospheric river of moisture into the Pacific Northwest starting
later this morning and progressing west to east into the northern
Rockies tonight. Snow levels will start quite high as QPF
increases, favoring the high Cascades initially. The cold front is
forecast to come ashore coastal WA around 06Z Sun and usher in
colder air aloft as snow levels crash to around 4500-5500ft (north
to south) along the WA Cascades as QPF rates decrease. However,
this will bring accumulating snow to the higher passes (e.g.,
Washington Pass/SR-20, elevation 5477ft) before moisture moves out
of the region around Monday morning. Into the northern Rockies,
snow levels around 6000-8000ft will fall to around 5000ft as snow
winds down later on Monday. The Bitterroots, Lewis Range, Absaroka,
and Tetons are forecast to see minor-to-moderate snowfall amounts
though some areas in NW MT may see over a foot (esp above 7000ft).
WPC probabilities for at least 8 inches of snow days 1-2 are >50%
above 5500ft or so and "plowable" snow (~2") down to around 4500ft
in the WA Cascades.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Fracasso

$$

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FOUS11 KWBC 181908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Sat Oct 18 2025

Valid 00Z Sun Oct 19 2025 - 00Z Wed Oct 22 2025

...Pacific Northwest and Northern Rockies...
Days 1-2...

A large, yet weakening, northeast Pacific storm system will direct
its cold front and attendant atmospheric river at the Pacific
Northwest tonight and Sunday morning. ECMWF PWATs are above the
90th percentile tonight and the IVT tops out around 800 kg/m/s.
This same moisture source looks to spill over into eastern WA,
northern ID, western MT, and northwest WY late tonight and into
Sunday. The strongest lift at mid-upper levels occurs overnight and
into Sunday morning as sharply decreasing heights and 500mb PVA
allows for heavier snowfall rates (1-2"/hr in some cases) and
falling snow levels. The cold front is expected to come ashore
around 06Z tonight, which will coincide with a gradual decrease in
QPF at the same time as snow levels steadily decrease to around
5,000ft. Some of the higher passes (such as Washington Pass/SR-20,
elevation 5,477ft) will be at risk of receiving hazardous snowfall accumulations tonight and through Sunday morning. Farther east,
snow levels will range generally between 6,000-8,000ft (closer to
6,000ft farther north, closer to 8,000ft in the Tetons and Wind
River Range) but some areas as low as 5,000ft in the ID Panhandle
and Lewis Range could see minor-to- moderate snowfall totals. Snow
will linger into Sunday night for the Northern Rockies's ranges
before tapering off Monday morning.

WPC probabilities for >8" of snowfall are moderate-to-high (50-80%)
in the northern WA Cascades and moderate (40-70%) in Bitterroots
and Lewis Range above 6,000ft. Anywhere between 6-12" of snowfall
is possible around Glacier Nat'l Park through Monday morning. The
WSSI does show generally Moderate Impacts around the Glacier Nat'l
Park, with some of the higher peaks potentially dealing with Major
Impacts. Expect icy and hazardous travel conditions in the higher
peaks of the Cascades and Northern Rockies.

The probability of significant freezing rain across CONUS is less
than 10 percent.

Mullinax



$$

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FOUS11 KWBC 190627
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 AM EDT Sun Oct 19 2025

Valid 12Z Sun Oct 19 2025 - 12Z Wed Oct 22 2025

...Pacific Northwest and Northern Rockies...
Day 1...

A cold front is moving quickly through Washington this morning
with its moisture plume aimed at the Cascades. This front will
continue to move eastward at a quick pace due to the progressive
yet still amplified upper pattern. Well above normal moisture
levels (PW anomalies >90th percentile) in the warm sector will
favor high snow levels ahead of the front (>7000ft) coincident with
the heavier QPF. This will limit snow accumulation to the highest
mountain peaks before snow levels drop sharply behind the front to
4500-5000ft. To the east, snow will spread across the northern
Rockies (northern Idaho/northwest Montana and into western WY) this
morning in advance of the cold front. High snow levels initially

8000ft will fall to around 5000-6000ft this afternoon. The quick

movement of the system will limit duration of the snow, and nearly
all the snow will clear the area by late Monday morning.

WPC probabilities for >8" of snowfall are >50% in the northern WA
Cascades above about 5000ft and will include Washington Pass
(SR-20) at nearly 5500ft elevation. To the east, WPC probabilities
for >8" of snowfall are >50% in the Bitterroots and Lewis Range
above 5000-6,000ft. Probabilities are lower over western Wyoming --
generally <40%.


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso



$$

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FOUS11 KWBC 191809
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
209 PM EDT Sun Oct 19 2025

Valid 00Z Mon Oct 20 2025 - 00Z Thu Oct 23 2025

...Pacific Northwest and Northern Rockies...
Day 1...

Radar and IR satellite composite are doing a great job with
identification of the progressive cold front migrating through the
interior Northwest CONUS with snow likely falling in-of the Lewis
and Bitterroot ranges this morning. Frontal progression will
continue to move swiftly to the southeast with frontal proxy
likely to encounter the Absaroka down through the Wind River Range
by later this afternoon and evening leading to crashing snow levels
and eventual snowfall. High snow levels will initially begin

8000ft, falling to around 5000-6000ft in wake of the front cold

front. The quick movement of the system will limit duration of the
snow, but periods of moderate to heavy snow will still induce a
relatively solid accumulation before shutting off from northwest
to southeast overnight, clearing the area by late Monday morning.

WPC probabilities for >8" of snowfall are between 50-80% in the
Bitterroots and Lewis Range above 5000-6,000ft. Probabilities are
lower over western Wyoming -- generally <40% with the strongest
signals targeted >8000ft. Highest totals will be focused over the
Lewis Range where >12" hovers between 40-70% probability just south
of Glacier National to the east of Flathead National Forest.

The probability of significant freezing rain across CONUS is less
than 10 percent.

Kleebauer/Fracasso






$$

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FOUS11 KWBC 200551
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
151 AM EDT Mon Oct 20 2025

Valid 12Z Mon Oct 20 2025 - 12Z Thu Oct 23 2025

...Northern Rockies...
Day 1...

At the start of the period this morning, the upper trough axis
will be exiting the Rockies with heights building in quickly this
afternoon to Montana/Wyoming. Lingering mainly upslope-driven snow
this morning will end by the afternoon over parts of western
Montana into the Big/Little Belts, Absarokas, and Bighorns. WPC
probabilities for at least an additional 4 inches of snow are
20-60% here and some high mountains peaks could see another 6
inches of snow.

Elsewhere, light snow is expected over the CO Rockies this morning
near the cold front before ending this afternoon. No appreciable
snow is expected until Wednesday over the Sierra as an upper low
moves ashore but snow levels there will be very high (>9000ft).


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso



$$

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FOUS11 KWBC 201800
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 PM EDT Mon Oct 20 2025

Valid 00Z Tue Oct 21 2025 - 00Z Fri Oct 24 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Kleebauer


$$

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FOUS11 KWBC 210629
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Tue Oct 21 2025

Valid 12Z Tue Oct 21 2025 - 12Z Fri Oct 24 2025

...CO Rockies...
Day 3...

An upper low in the Pacific (southwest of California) will move
into the Golden State on Wednesday, bringing some light snow to the
high Sierra (above 9500ft). On Thursday, it will cross through the
Four Corners region with antecedent LFQ jet ascent over
southwestern to central Colorado. Moisture levels will rise just a
bit to around +1 sigma (PW values 0.4-0.5 inches) though snow
levels will be high -- >10,000ft to start then decreasing overnight
Thursday into Friday morning to around 9500ft. At the end of this
forecast period, the upper low will likely be centered over south
central CO with snow continuing but starting to wind down. WPC
probabilities for at least 6 inches of snow are at least 40% above
11,000ft. This will likely impact high passes such as
I-70/Eisenhower Tunnel.



The probability of significant ice across the CONUS is less than
10 percent.

Fracasso



$$

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FOUS11 KWBC 211936
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Tue Oct 21 2025

Valid 00Z Wed Oct 22 2025 - 00Z Sat Oct 25 2025

...High Sierra Nevada...
Day 1.5...

An upper low off southern CA coast tracks over the southern Sierra
Nevada Wednesday. Snow levels dip to around 9500ft under the low
Wednesday afternoon with moderate snow rates (up to an inch per
hour according to the 12Z HREF) and 20-30% Day 1.5 snow
probabilities for >6" in the High Sierra mainly Wednesday
afternoon.


...Colorado Rockies...
Day 2.5...

The upper low southwest of California this afternoon will track
east to the Four Corners through Thursday before slowing and
opening into a trough over the Southern Rockies through Friday. A
decent plume of Pacific moisture streaming ahead of the low will
allow moderate precipitation rates with snow levels around 10,000ft
over the CO Rockies Thursday afternoon and evening. Day 2.5 WPC
probabilities for >6" are 20-50% in the northern San Juans as well
as the Elk Mtns, Sawatch Range, and Mosquito Range in central
Colorado, including high passes such as I-70/Eisenhower Tunnel.


...North Cascades...
Day 3...

A brief shortwave trough passage midday Wednesday brings snow
levels down to 7000ft over the North Washington Cascades. A much
more expansive and stronger trough approaches the Pacific Northwest
coast on Friday with high snow levels in the initial moisture
surge, but dropping to around 6000ft by Friday afternoon. Heavy
snow can be expected Friday on the highest Washington Cascade
peaks.



The probability of significant ice across the CONUS is less than
10 percent.

Jackson



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FOUS11 KWBC 220624
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 AM EDT Wed Oct 22 2025

Valid 12Z Wed Oct 22 2025 - 12Z Sat Oct 25 2025

...High Sierra Nevada...
Day 1...

An upper low just southwest of Southern California this morning
will move inland and cross the southern Sierra Nevada this evening,
brining some light snow to the high mountains. Snow levels around
10,000ft will only fall to around 9500ft as the upper low passes
through. WPC probabilities for at least 6 inches of snow are low
(10-30%) above 10,000-10,500ft.


...Colorado Rockies...
Day 2...

On Thursday, the CA upper low will track into the Four Corners
region with some broad jet-divergence atop a moistening mid/lower-
layer. PWs will climb to near 0.50 inches with upslope-driven snow
into the San Juans northward to the central CO ranges. Snow levels
will be high -- 11,000ft to start on Thursday then falling to
around 9500ft Friday morning as the upper low moves. Still, this
will affect the high mountain passes such as I-70/Eisenhower
Tunnel. WPC probabilities for at least 6 inches of snow are >50%
above about 11,000ft. The highest peaks in the Sawatch Range

12,000ft) may see more than 8-10 inches of snow (30-60% chance).

...Northern Cascades...
Day 3...

Deep Northeastern Pacific trough on Friday will strong cold front
into WA and OR. Higher snow levels ahead of the front (6000-7000ft)
will sharply drop overnight into early Saturday to around
5000-6000ft (north to south along the WA to OR Cascades). WPC
probabilities for at least 6 inches of snow through 12Z Sat are

50% above about 6000ft in the WA Cascades with more snow to follow

into the weekend.


The probability of significant ice across the CONUS is less than
10 percent.

Fracasso


$$

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FOUS11 KWBC 221854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Wed Oct 22 2025

Valid 00Z Thu Oct 23 2025 - 00Z Sun Oct 26 2025

...Colorado Rockies...
Days 1-2...

On Thursday, an upper low over CA tracks into the Four Corners
region with some broad jet-divergence atop a moistening mid/lower-
layer. PWs will climb to near 0.50 inches with upslope-driven snow
into the San Juans northward to the central CO ranges. Snow levels
will be high, around 11,000ft, to start on Thursday then falling to
around 9000ft Friday morning as the upper low moves overhead.
While snow levels will generally be high enough to avoid producing
snow within the valleys below 9,000ft, this will affect the high
mountain passes such as I-70/Eisenhower Tunnel. WPC probabilities
for at least 6 inches of snow are >50% above about 11,000ft. The
highest peaks in the Sawatch Range (>12,000ft) may see more than
8-10 inches of snow (30-60% chance).

...Northern Cascades...
Day 3...

A deep Northeastern Pacific trough will direct a strong cold front
and attendant atmospheric river into WA and OR on Friday that
persists through Saturday. Embedded within the longwave trough are
two shortwave disturbances that will foster strong vertical ascent
via 500mb PVA Friday night and again on Saturday. Higher snow
levels ahead of the front (6000-7000ft) will sharply drop overnight
into early Saturday to around 5000-6000ft (north to south along
the WA to OR Cascades) as mid-upper level height falls ensue Friday
night. By the time the core of the upper trough makes it over
western WA, snow levels over the Olympics are expected to dip to
just below 4,000ft AGL, with snow levels along the Cascades between 4,000-4,500ft. Snow levels should dip below 4,000ft along the
Cascades by Saturday evening, making possible for light
accumulations along some of the WA Cascade passes. WPC
probabilities for at least 4 inches of snow through 00Z Sunday are

50% above about 6000ft in the WA Cascades with more snow to

follow into the weekend.


The probability of significant ice across the CONUS is less than
10 percent.

Fracasso/Mullinax





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FOUS11 KWBC 230705
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Thu Oct 23 2025

Valid 12Z Thu Oct 23 2025 - 12Z Sun Oct 26 2025

...Colorado Rockies...
Day 1...

A compact upper low will traverse the Four Corners today, pushing
height falls and accompanying modest mid-level diverge into
Colorado through tonight. This ascent will work into moistening
low-levels as SW flow pushes PWs to above the 90th percentile (in
some places above the 95th percentile) of the CFSR climatology. The
combination of synoptic lift and periodic upslope flow into this
saturating column will drive periods of moderate snowfall into the
terrain of the Colorado Rockies. The combination of high snow
levels (generally 10,000 - 11,000 ft) with modest total ascent and
peak precipitation occurring during daytime hours should limit
overall snowfall. However, WPC probabilities are high (>70%) for at
least 4 additional inches of snow in the higher terrain, especially
across the Sawatch and Mosquito Ranges where locally 12" of snow is
possible (10-30% chance).


...Pacific and Interior Northwest...
Days 2-3...

An active pattern begins in the Northwest starting late Friday and
persists through the weekend as an atmospheric river (AR) surges
into the Pacific Northwest and then spreads moisture inland.

This AR will be created by an impressive mid and upper level trough
which will amplify over the Northeast Pacific ocean and then shunt
southeast, reaching the coast by Sunday morning. There is very good
agreement amongst both the ECENS and GEFS members for resulting IVT
approaching 750 kg/m/s pushing onshore D2, suggesting a strong AR
event for the region. As this AR pushes southeast in response to
the approach of the trough, forcing for ascent will additionally
increase through resultant height falls/divergence downstream of
the primary trough, and thanks to an accelerating upper jet streak
placing favorable LFQ diffluence into the Northwest on Saturday. At
the same time, this evolution will drive a frontal wave and
associated cold front eastward into the Northern Rockies by
Saturday morning, with a secondary impulse traversing the region
during D3. Together, this will produce a long period of moderate to
robust ascent, with lowering snow levels.

Initially, snow levels during D2 will be generally 6000-7000 ft, so
above all but the highest passes. However, a rapid fall in snow
levels behind the first front will combine with steepening lapse
rates beneath the upper trough and impressive mid-level confluence,
suggesting intense ascent into favorable upslope terrain. This
should allow for snow levels to crash, and the NBM indicates snow
levels falling to as low as 3500 ft in the Cascades and 4500 ft in
the Northern Rockies by 12Z/Sunday. It is possible with the strong
ascent and steep lapse rates, snow levels will be even lower than
that, reflected by NBM 10th percentile snow levels falling to 2500
ft/4000 ft, respectively. This will be accompanied by climbing
SLRs, with early season, abov-climo SLR likely the latter half of
the event.

With the incoming AR, snowfall probabilities gradually increase and
expand across the region. For D2, WPC probabilities for more than 4
inches are above 50% only in the highest peaks of the Cascades.
However, during D3 as moisture expands and snow levels crash, WPC
probabilities for 4+ inches reach above 70% across much of the WA
and OR Cascades above 4000 ft, and extend into portions of the
Salmon River and Sawtooth Ranges as well. Additionally, as snow
levels crash, several inches of snowfall will create hazardous
travel at many of the Cascade Passes including Stevens, Washington,
and Santiam Passes


The probability of significant ice across the CONUS is less than
10 percent.

Weiss


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FOUS11 KWBC 231908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Thu Oct 23 2025

Valid 00Z Fri Oct 24 2025 - 00Z Mon Oct 27 2025

...Colorado Rockies...
Day 1...

A compact upper low traversing the Central Rockies this afternoon
and overnight will result in height falls and modest mid-level
divergence over Colorado. The increased vertical velocities within
the atmospheric column will work to moisten low-levels as SW flow
pushes PWs above the 90th percentile (some places above the 95th
percentile) of the CFSR climatology. The combination of synoptic
lift and periodic upslope flow into this saturating column will
drive periods of moderate snowfall into the terrain of the Colorado
Rockies. The combination of high snow levels (generally 10,000 -
11,000 ft) with modest total ascent and peak precipitation
occurring during daytime hours should limit overall snowfall.
However, WPC probabilities are moderate-to-high (40-70%) for at
least 4 additional inches of snow in the higher terrain, especially
across the Sawatch and Mosquito Ranges where locally 12" of snow
is possible (10-30% chance).


...Pacific and Interior Northwest...
Days 2-3...

An active pattern begins in the Northwest starting late Friday and
persists through the weekend as an atmospheric river (AR) surges
into the Pacific Northwest and then spreads moisture inland.

This AR develops due to an impressive mid and upper level trough
amplifying over the Northeast Pacific ocean that becomes shunt
southeast, reaching the Pacific Northwest coast by Sunday morning.
Both the ECENS and GEFS members depict an IVT approaching 750
kg/m/s pushing onshore on Friday, suggesting a strong AR event is
likely to impact the region. As the AR pushes southeast in response
to the approach of the trough, forcing for ascent will
additionally increase through resultant height falls/divergence
downstream of the primary trough, and thanks to an accelerating
upper jet streak placing favorable LFQ diffluence into the
Northwest on Saturday. At the same time, this evolution will drive
a frontal wave and associated cold front eastward into the Northern
Rockies by Saturday morning, with a secondary impulse traversing
the region during D3. Together, this will produce a long period of
moderate to robust ascent, with lowering snow levels.

Initially, snow levels during D2 will be generally 6000-7000 ft, so
above all but the highest passes. However, a rapid fall in snow
levels behind the first front will combine with steepening lapse
rates beneath the upper trough and impressive mid-level confluence,
suggesting intense ascent into favorable upslope terrain. This
should allow for snow levels to crash, and the NBM indicates snow
levels falling to as low as 3500 ft in the Cascades and 4500 ft in
the Northern Rockies by 12Z/Sunday. It is possible with the strong
ascent and steep lapse rates, snow levels will be even lower than
that, reflected by NBM 10th percentile snow levels falling to 2500
ft/4000 ft, respectively. This will be accompanied by climbing
SLRs, with early season, abov-climo SLR likely the latter half of
the event.

With the incoming AR, snowfall probabilities gradually increase and
expand across the region. For D2, WPC probabilities for >6" are
above 50% only in the highest peaks of the Cascades. However,
during D3 as moisture expands and snow levels crash, WPC
probabilities for 6"+ exceed 70% across much of the WA and OR
Cascades above 4000 ft, and extend into portions of the Salmon
River and Sawtooth Ranges as well. Additionally, as snow levels
crash, several inches of snowfall will create hazardous travel at
many of the Cascade Passes including Stevens, Washington, and
Santiam Passes.


The probability of significant ice across the CONUS is less than
10 percent.

Weiss/Mullinax





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FOUS11 KWBC 240757
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Fri Oct 24 2025

Valid 12Z Fri Oct 24 2025 - 12Z Mon Oct 27 2025


...Pacific Northwest through the Central Rockies...
Days 2-3...

Complex mid-level evolution will result in active weather expanding
across the Northwest and eventually into the Central Rockies
through the weekend.

The primary driver of this development will be an anomalous and
persistent 500mb low over the Northeast Pacific that will gradually
advect east to come onshore near the Olympic Peninsula Sunday
morning. Downstream of this feature and before the onshore
movement, impressive and pinched SW flow will funnel an atmospheric
river (AR) into the Northeast characterized by IVT which may exceed
750 kg/m/s (50-70% chance). This will rapidly moisten the
atmospheric column, and as forcing for ascent increases through
height falls, PVA, and the LFQ of an accompanying Pacific jet
streak, periods of moderate to heavy rainfall will result from
Friday night through Sunday night. There are modest discrepancies
among the various deterministic models and accompanying ensembles,
but in general the consensus is good for significant rainfall
across much of the Pacific Northwest, with moisture spilling well
eastward Saturday night, with a second round possible Sunday night
as a secondary, more zonally oriented and weaker, AR pivots
eastward.

Initially, the pronounced SW flow will warm the column such that
snow levels are above most passes (6000-8000 ft). However, a cold
front accompanying the first wave embedded within the AR (or just
behind it) will combine with the height falls to crash snow levels
to as low as 4000 ft by Saturday morning in the Pacific Northwest,
with the advection of this cold front eastward driving snow levels
down to 4000-4500 ft in the Northern Rockies by Sunday morning. The
secondary surge of moisture and continued cooling as a low pressure
moves into British Columbia will help drive snow levels down even
further late D2 into D3, with the NBM featuring mean snow levels as
low as 3000 ft late Sunday in the Pacific Northwest (rising to
around 5000 ft in WY). However, despite forcing weakening during
this time, steep lapse rates may allow precipitation to drag cold
air even further down towards the surface, so once again the
NBM10th percentile for snow level, around 2500 ft in WA to around
3500 ft in MT/WY may be more realistic as the level for at least
minor accumulating snow and accompanying transportation impacts.

This will be a long-lasting event that will occur in waves, so
impacts will be drawn out, and the heaviest snow is likely where
upslope flow is most pronounced. Day 1 /Friday and Friday night/ is
likely to be the quietest of the period and WPC probabilities for
4+ inches are modest (just 10-20%) and confined to the highest WA
Cascades. By D2, however, precipitation and snowfall become much
more expansive, and WPC probabilities become high (>70%) for 6+
inches along the spine of the WA and OR Cascades, and spill over
into the Sawtooth/Salmon River range of ID, primarily above 5000
ft. During D3 as the snow levels fall more considerably, WPC
probabilities for an additional 6+ inches continue above 70% in
much of these same areas, and expand into the NW WY ranges as well.
With snow levels falling, impacts to the passes become more notable
late D2 into D3 as well, with moderate impacts likely across the
Cascades including at Santiam and Stevens Passes.


The probability of significant ice across the CONUS is less than
10 percent.

Weiss



$$

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FOUS11 KWBC 241929
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Fri Oct 24 2025

Valid 00Z Sat Oct 25 2025 - 00Z Tue Oct 28 2025


...Pacific Northwest through the Central Rockies...
Days 1-3...

A deep low remains over the Gulf of Alaska through Saturday night.
An initial shortwave trough, which has been directing an
atmospheric river (AR) into eastern OR/WA today, crosses the coast
this evening bringing rapidly falling heights and cooler
conditions. Snow levels drop from around 8000ft currently to around
5000ft on the OR/WA Cascades by 06Z with heavy snow limited to the
higher Cascades. The QPF will then have brief reprieve overnight
from minor ridging ahead of the main shortwave trough axis that
crosses the OR/WA coast midday Saturday. The second surge in
moisture arrives as a thump Saturday morning ahead of that second
axis with snow levels around 4000ft in WA, 5000ft in OR, and 7000ft
in northern CA and the Sawtooths of ID which are in the AR axis.
This surge then progresses inland, reaching the MT Rockies Saturday
evening and overnight for the western WY Rockies.

A third shortwave trough axis crosses the OR/WA coast midday Sunday
with slow ridging then through Monday in continued onshore flow.
Snow levels decline through Sunday, reaching 3500ft from WA through
western MT, 4500ft from OR through northwest WY, and about 5000ft
in northern CA. Therefore this will be a long- lasting event with
drawn- out impacts. The heaviest snow is expected on the Cascades
which are orthogonal to the onshore flow. Moderate impacts become
likely across the higher Cascades passes including Stevens and
Santiam Saturday night.

Day 1.5 (Saturday/Saturday night) WPC snow probabilities for >12"
are 40-70% for the higher Cascades and Sawtooths with similar
percentages for >24" in the highest Cascades.

Day 2.5 probs for an additional >6" are 40-70% for the Cascades,
Bitterroots and Sawtooths, as well as the Absarokas/Tetons, and
Wind Rivers. Snow levels decrease to around 7000ft in southern
WY/northern CO Sunday night with moderate rates and Day 3 snow
probs of 20-40% in the Park Range of CO.


The probability of significant ice across the CONUS is less than
10 percent.

Jackson


$$

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FOUS11 KWBC 250818
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Sat Oct 25 2025

Valid 12Z Sat Oct 25 2025 - 12Z Tue Oct 28 2025


...Pacific Northwest through the Central Rockies...
Days 1-3...

The core of the atmospheric river (AR) which has been progged to
lift into the Northwest for several days now will be advecting
onshore this morning and dropping south into CA and the Great Basin
through the day. IVT exceeding 500 kg/m/s is likely (>70% chance)
which will also be above the the 99th percentile according to NAEFS
within a narrow channel focused from CA into the Northern Rockies.

Into this moistening column, ascent will maximize downstream of the
primary upper low which will track northeast into British Columbia
tonight. South of the core of this low, impressively confluent
mid-level flow will help persist moisture advection such that much
of the region will experience above normal PWs leading to periods
of moderate to heavy precipitation as height falls, PVA, and
diffluence combine atop the area. This will yield two round of
heavy precipitation, the first today, and the second Sunday aftn
and Sunday night in response to secondary shortwave energy lifting
onshore near Oregon. Although there continue to be intensity
differences among the various global guidance, the end result in a
long period of heavy precipitation, with snow becoming more
widespread as snow levels crash.

Initially, snow levels will remain high, generally around 7000 ft
within the core of the AR, but falling to 4000-5000 ft behind the
accompanying cold front and in response to the associated height
falls. Snow levels will then continue to drop on Sunday with the
secondary shortwave energy, becoming as low as 3500 ft in the
Cascades and 4500 ft farther south and east. However, with steep
lapse rates and periods of impressive omega, cold air could be
dragged down by heavy precipitation rates (snowfall rates above
1"/hr at times) such that accumulating snow may occur as low as
2500-3000 ft, or near the NBM 10th percentile. This will enhance
the areal footprint of snowfall, and also lead to more widespread
pass level impacts Saturday night and Sunday.

The heaviest and most widespread snowfall this period is expected
today through Sunday. For today, WPC probabilities are high (>70%)
for 6+ inches of snow across the spine of the Cascades of OR and
WA, as well as into the higher terrain of the Olympics and Sawtooth
ranges. Locally, 1-2 feet of snow is likely in the highest terrain.
During D2, the snow intensity begins to wane across the Pacific and
Interior Northwest, although WPC probabilities suggest a moderate
to high chance (40-70%) for an additional 6+ inches in many of
these same areas. However, in general the heaviest snowfall is
expected to shift into the area around Yellowstone NP including the
Wind River and Teton ranges where WPC probabilities for 8+ inches
of snow on D2 peak above 70%. With snow levels falling late D1 and
through D2, pass-level impacts are likely with significant snowfall accumulations probable at both Stevens and Santiam Passes.

The probability of significant ice across the CONUS is less than
10 percent.


Weiss


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FOUS11 KWBC 251941
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 PM EDT Sat Oct 25 2025

Valid 00Z Sun Oct 26 2025 - 00Z Wed Oct 29 2025


...Pacific Northwest to the Central Rockies...
Days 1-2...

Main shortwave trough axis rounding low from deep Gulf of Alaska
low is crossing the OR/WA coast this afternoon. Snow levels are
quickly dropping to around 4500ft over the Cascades and will drop
to around 5000ft over the Northern Rockies this evening. A
reinforcing shortwave trough axis crosses the OR/WA coast Sunday
morning with continued onshore flow with decreasing precip rates
then through Sunday night.

Heavy snow rates of 1-2"/hr persist through tonight along the
Cascades per the 12Z HREF which combined with snow levels dropping
to around 3500ft should result in moderate winter weather impacts
for most mountain passes in the Cascades tonight. One to two feet
of snow should occur tonight in the Cascades well above pass level.

The precipitation focus shifts inland Sunday with moderate to
locally heavy rates in terrain of the northern Rockies (MT/ID/WY)
persisting into Monday morning. Snow levels will be around 3500ft
in the Bitterroots and north, around 5000ft in the Sawtooths of ID,
and 5500ft around Yellowstone. Day 1.5 snow probabilities for >6"
are 30-60% through these ranges and over 80% in the Wind River in
WY.


The probability of significant ice across the CONUS is less than
10 percent.


Jackson



$$

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FOUS11 KWBC 260900
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
500 AM EDT Sun Oct 26 2025

Valid 12Z Sun Oct 26 2025 - 12Z Wed Oct 29 2025


...Pacific Northwest to the Central Rockies...
Days 1-2...

The primary shortwave axis will be positioned well inland, near
the Northern Rockies, to begin the period /12Z Sunday/, but a
secondary impulse and accompanying surface wave will move onshore
near the OR/CA border this evening. The accompanying pinched and
confluent mid-level flow will continue to advect higher moisture
onshore, leading to a second wave of heavy precipitation moving
from the Cascades early today into the Northern Rockies by early
Monday.

This second wave of precipitation will occur behind the primary
cold front, and during a period of continued height falls, so snow
levels will fall steadily through D1. The latest NBM snow level
forecasts have trended downward, reaching as low as 2000 ft in the
eastern Cascades, to around 3500 ft in parts of OR/MT/ID. This will
occur in tandem with waves of precipitation, such that even though precipitation intensity may be less than what occurred Saturday,
pass level impacts will be more substantial due to the lower snow
levels. This wave moves quickly east, however, and by Monday night precipitation should generally wane across the region.

WPC probabilities are high (>70%) for 6+ inches across the Cascades
and into portions of the Salmon River ranges D1 before waning
quickly during D2. Passes will likely become hazardous D1 due to
low snow levels, especially around Stevens and Santiam Passes in
the Cascades.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss


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FOUS11 KWBC 261939
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Sun Oct 26 2025

Valid 00Z Mon Oct 27 2025 - 00Z Thu Oct 30 2025


...Cascades and Northern/Central Rockies...
Day 1...

The third and final shortwave trough axis with the troughing over
the Northwest the past couple of days is pushing over the OR coast
this afternoon. This axis reaches central MT by 18Z Monday and will
provide the focus for moderate to locally heavy snow over the
Cascades and northern Rockies that mainly tapers off for the
Cascades Monday morning and Monday evening for the northern
Rockies. Snow levels drop further under this trough, to around
3000ft in the WA Cascades tonight and the Bitterroots Monday
morning, and around 3500ft in the OR Cascades through Sawtooths of
ID and around Yellowstone (Absarokas, Tetons, Wind River) and about
4500ft for the Bighorns.

Day 1 WPC probabilities are high (50-80%) for >8" for the Tetons,
southern Absarokas, Wind River, and Bighorns while moderate
(40-60%) for >6" for the higher Cascades, Blue Mtns of OR,
Bitterroots and Lewis Range, Uinta of UT and the Medicine Bow/Park
Range along the WY/CO border.

Lee-side troughing should allow some higher elevation snow in
eastern WY and the Black Hills Monday evening.


...Washington Cascades...
Day 3...

A potent, but progressive low pushes across the BC coast Tuesday
night with a trough axis extending south over Washington State.
High snow levels around 8000ft Tuesday afternoon in the elevated
moisture plume quickly crash to around 4500ft by the time the
trough crosses and precip cuts off. Day 3 snow probabilities for

6" are 20-40% around North Cascades NP.

The probability of significant ice across the CONUS is less than
10 percent.


Jackson



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FOUS11 KWBC 270735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Mon Oct 27 2025

Valid 12Z Mon Oct 27 2025 - 12Z Thu Oct 30 2025


...Northern/Central Rockies...
Day 1...

Persistent moisture on confluent west to east flow impinging into
the Northwest will be acted upon by height falls/PVA through the
last in this series of shortwaves moving from ID into MT and WY
today into tonight. This feature will be quickly followed by
shortwave ridging in its wake, bringing an end to precipitation by
the end of D1. Snow levels will remain relatively low, around 3500
ft west, 4500 ft east, with several inches of snowfall likely above
these levels, leading to at least scattered pass level impacts.
WPC probabilities D1 indicate a high chance (>70%) for additional
snowfall above 6" in the Tetons and Big Horns, with light snow
accumulating to a few inches likely in the CO Rockies, the
Northern Rockies, and even into the higher Black Hills.


...Washington Cascades...
Day 2...

A potent, but progressive low pushes across the BC coast Tuesday
night with a trough axis extending south over Washington State. A
brief period of enhanced moisture noted in regional soundings will
result in transient but heavy precipitation, driven by a narrow
corridor of intense 700-600mb fgen late Tuesday night. The
strongest fgen appears to efficiently intersect the DGZ, which will
deepen as colder air floods eastward behind the accompanying
shortwave. While the heaviest precip will likely occur with snow
levels around 8000 ft limiting pass-level impacts, they will crash
quickly, aided by the heavy precipitation rates, to around 4500 ft
before precipitation wanes. This results in WPC probabilities for
more than 4" of snow reaching 70-90% across the highest terrain of
the WA Cascades, with a few inches of snow likely at Washington
Pass.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss


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FOUS11 KWBC 271855
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Mon Oct 27 2025

Valid 00Z Tue Oct 28 2025 - 00Z Fri Oct 31 2025


...Northern/Central Rockies...
Day 1...

Remaining moisture on the backside of a departing trough will
wring out a few more inches of snow tonight over northwestern
Montana where WPC probabilities for at least another 4 inches of
snow after 00Z/28 are low (<40%).


...Washington Cascades...
Day 2...

A rapidly-deepening and strong closed low over the northeastern
Pacific tonight/Tuesday will start to weaken as it moves ashore
British Columbia tomorrow night. Mild temperatures will flood the
Pacific Northwest ahead of the cold front with snow levels as high
as 8000-9000ft 06Z Wednesday. However, snow levels will crash quite
smartly by 12Z as precipitation starts to decrease and end by the
conclusion of day 2 (00Z/30). There will be a brief but impressive
period of heavy snow invading lower elevations (down to about
4500ft) which will impact the higher Washington Pass/SR-20. WPC
probabilities for at least six inches of snow are >50% above about
5000ft depending on how quickly snow levels fall coincident with
moderate QPF.


The probability of significant ice across the CONUS is less than
10 percent.

Fracasso



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FOUS11 KWBC 280659
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Tue Oct 28 2025

Valid 12Z Tue Oct 28 2025 - 12Z Fri Oct 31 2025


...Washington Cascades...
Day 1...

A potent surface low will slowly weaken as it lifts into British
Columbia tonight. Downstream of this feature, impressively
confluent and warm mid-level flow will surge elevated PWs northeast
into the Cascades, with snow levels rising to around 8000 ft.
However, as the attendant cold front drapes into WA/OR late
tonight, it will be accompanied by falling snow levels and
impressive mid-level fgen into a deepening DGZ. This suggests that precipitation will gradually transition from rain to a brief but
intense period of heavy snow reflected by HREF snowfall rate
probabilities peaking above 70% for 1"/hr. Snow levels falling to
around 4500 ft may actually be realized a bit lower than that due
to the intensity of this snowfall dragging down colder air, so the
higher passes such as Washington Pass will likely experience
hazardous travel. Total snowfall is likely to be generally modest,
but WPC probabilities indicate a moderate risk (50% chance) of more
than 6 inches in the highest terrain of the northern WA Cascades,
with a few inches likely at Washington Pass.

The probability of significant ice across the CONUS is less than
10 percent.

Weiss


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FOUS11 KWBC 281950
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Tue Oct 28 2025

Valid 00Z Wed Oct 29 2025 - 00Z Sat Nov 01 2025


...Washington Cascades...
Day 1...

Forecast thinking remains mostly unchanged as a potent surface low
is forecast to slowly weaken as it lifts into British Columbia
tonight. Downstream of this feature, impressively confluent and
warm mid-level flow will surge elevated PWs northeast into the
Cascades, with snow levels rising to around 8000 ft within the
pre-frontal airmass. However, as the attendant cold front drapes
into WA/OR late tonight, it will be accompanied by falling snow
levels and impressive 700-500 mb frontogenesis superimposed with a
deepening DGZ. This suggests that precipitation will gradually
transition from rain to a brief but intense period of heavy
mountain snow, reflected by 12z HREF snowfall rate probabilities
now above 80% for 1"/hr in the 8-10z timeframe. Snow levels falling
to around 4500 ft may actually be realized a bit lower than that
due to the intensity of this snowfall dragging down colder air, so
the higher passes such as Washington Pass will likely experience
hazardous travel. Total snowfall is likely to be generally modest,
but WPC probabilities of more than 6 inches have increased since
the previous to 80-90% in the highest terrain of the northern WA
Cascades, with a few inches likely at Washington Pass.

The probability of significant ice across the CONUS is less than
10 percent.

Asherman/Weiss





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FOUS11 KWBC 290540
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
140 AM EDT Wed Oct 29 2025

Valid 12Z Wed Oct 29 2025 - 12Z Sat Nov 01 2025


...Washington Cascades...
Day 3...

An impressive shortwave will again lift towards British Columbia
late Friday and Friday night, channeling moisture within confluent
SW mid-level flow into the Pacific Northwest. Both IVT and PW
anomalies from NAEFS are progged to exceed the 97th percentile
within the CFSR climatology, suggesting that precipitation may
become heavy very late on D3. However, the accompanying WAA driving
this moisture plume northeastward will surge snow levels to
8000-9000 ft, and any cold advection associated with a surface
front will be delayed until beyond this forecast period. Still,
some high elevation snow is likely in the northern WA Cascades,
reflected by WPC probabilities reaching up to 50% for 6+ inches,
but impacts should remain above pass level into Saturday.

The probability of significant ice across the CONUS is less than
10 percent.

Weiss








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FOUS11 KWBC 291949
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Wed Oct 29 2025

Valid 00Z Thu Oct 30 2025 - 00Z Sun Nov 02 2025


...Washington Cascades...
Day 3...

Another strong shortwave will lift towards British Columbia late
Friday and Friday night, channeling moisture within a zonal Pacific
jet into the Pacific Northwest. Both IVT and PW anomalies from
NAEFS are progged to exceed the 97th percentile within the CFSR
climatology, suggesting that precipitation may become heavy very
late on D3. However, the accompanying WAA driving this moisture
plume northeastward will surge snow levels to 8000-9000 ft, and any
cold advection associated with a surface front will be delayed
until beyond this forecast period. This should limit appreciable snowfall
to the northernmost portions of the WA Cascades, with impacts still
expected to remain above pass level through Saturday.

The probability of significant ice across the CONUS is less than
10 percent.

Asherman/Weiss











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FOUS11 KWBC 300709
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Thu Oct 30 2025

Valid 12Z Thu Oct 30 2025 - 12Z Sun Nov 02 2025

...Washington Cascades...
Day 3...

A shortwave disturbance at the base of a massive longwave trough
positioned over the northeast Pacific will direct a highly
anomalous IVT topping 1,000 kg/m/s at the Pacific Northwest late
Friday night and into Saturday. There is no shortage of moisture
within the IVT as PWs approach 1.25" over western WA, which in some
instances tops the 99th climatological percentile per ECMWF SATs.
That said, the air-mass the IVT is ushering in is also rather mild
and antecedent boundary layer temperatures are not cold enough to
support heavy snowfall below 5,000ft south of US Route 2 and
Stevens Pass. Most passes should remain below the freezing level,
making rain the primary precipitation type below 5,000ft. The
Cascades north of US-2 above 5,000ft have the better odds (WPC
probabilities >4" between 10-30%) for locally heavier snowfall
totals.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax














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FOUS11 KWBC 302014
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Thu Oct 30 2025

Valid 00Z Fri Oct 31 2025 - 00Z Mon Nov 03 2025

...Washington Cascades...
Days 2-3...

A shortwave disturbance at the base of a massive longwave trough
positioned over the northeast Pacific will direct a highly
anomalous IVT topping 1,000 kg/m/s at the Pacific Northwest late
Friday night and into Saturday. There is no shortage of moisture
within the IVT as PWs approach 1.25" over western WA, which in some
instances tops the 99th climatological percentile per ECMWF and
NAEFS SATs. That said, the Pacific air-mass is also rather mild
and antecedent boundary layer temperatures are not cold enough to
support heavy snowfall below 5,000ft south of US Route 2 and
Stevens Pass. Most passes should remain below the freezing level,
making rain the primary precipitation type below 5,000ft. The
Cascades north of US-2 above 5,000ft maintain better odds for
locally heavy snowfall, where localized 50-80% probabilities of
exceeding 4 inches are noted this forecast cycle.


The probability of significant ice across the CONUS is less than
10 percent.

Asherman/Mullinax

















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FOUS11 KWBC 310706
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
306 AM EDT Fri Oct 31 2025

Valid 12Z Fri Oct 31 2025 - 12Z Mon Nov 03 2025

...Northern Appalachians...
Day 1...

The powerful storm system tracking over Quebec will generate
strong CAA at low-levels at the same time as a TROWAL pivots over
the Northern Appalachians. The depth of the atmosphere is
sufficiently saturated and cold enough to support periods of snow
at elevations above 1,500ft in the Adirondacks and above 2,000ft in
the Green and White Mountains. NWrly flow will support enhanced
upslope flow into some of the orographically favored mountain
ranges, thus aiding in more efficient dynamic cooling aloft. The
lowest 1,000ft of the boundary layer are likely to hover around or
slightly above 32F, which will make snow tough to accumulate during
the day on Friday. But as the sun sets, snow falling within a
marginaly-cold boundary layer should improve the chances for snow
to accumulate in the higher elevations. WPC probabilities do show
some low-to-moderate chances (10-40%) for snowfall totals >2" in
the Adirondacks, but probabilities for >4" of snowfall are topping
out around 10%. The WSSI does depict splotchy areas of Minor
Impacts (winter driving conditions, use caution while driving) in
the Adirondacks, Green, and White Mountains. One location that
could see locally heavy snowfall is Mount Washington where the
combination of strong winds and snowfall totals approaching 6"
could support Moderate Impacts.

...Washington Cascades...
Days 2-3...

A shortwave disturbance at the base of a massive longwave trough
positioned over the northeast Pacific will direct a highly
anomalous IVT topping 1,000 kg/m/s at the Pacific Northwest Friday
night and into Saturday. There is no shortage of moisture within
the IVT as PWs approach 1.25" over western WA, which in some
instances tops the 99th climatological percentile per ECMWF and
NAEFS SATs. That said, the Pacific air-mass is also rather mild and
antecedent boundary layer temperatures are not cold enough to
support heavy snowfall below 5,000ft south of US Route 2. Most
passes should remain below the freezing level, making rain the
primary precipitation type below 5,000ft. One exception may be
Stevens Pass, where some light snowfall totals are possible. The
Cascades north of US-2 above 5,000ft maintain better odds for
locally heavy snowfall, where 50-80% probabilities of exceeding 4
inches are depicted.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax




















$$

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FOUS11 KWBC 311901
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Fri Oct 31 2025

Valid 00Z Sat Nov 01 2025 - 00Z Tue Nov 04 2025

...Northeast Terrain...
Day 1...

Low pressure over northern New England lifts north to the Gulf of
St. Lawrence tonight. Wrap around/northwesterly flow on the back
side will support moist upslope flow through the Adirondacks,
Greens, and Whites. Snow levels drop from around 2000ft to 1000ft
this evening allowing increasing coverage of elevation based snow
accumulation through early Saturday morning. Day 1 snow
probabilities for >4" are 20-60% above 1500ft over those ranges.


...Washington Cascades...
Days 1-2...

A longwave trough extending from a low over the Gulf of Alaska
directs is directing highly anomalous IVT topping 1,000 kg/m/s (and
PW up to 1.25") at the Pacific Northwest through Saturday
morning. Snow levels remain high in this atmospheric river, around
9000ft over the northern Cascades, until a shortwave trough passage
Saturday afternoon brings heights down. A rapid drop in snow level
to 3000-4000ft before snow tapers off Saturday night allows some
impactful snow. Day 1.5 WPC snow probabilities for >6" are 30-60%
above at least 5000ft.


The probability of significant ice across the CONUS is less than
10 percent.

Jackson























$$

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FOUS11 KWBC 010723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Sat Nov 1 2025

Valid 12Z Sat Nov 01 2025 - 12Z Tue Nov 04 2025

...Washington Cascades...
Days 1 & 3...

A longwave trough entrenched over the northeast Pacific will direct
a continuous fetch of Pacific moisture and embedded storm systems
at the Pacific Northwest and British Columbia over the next 5-7
days. For the purposes of this short range discussion, Days 1 and 3
pose some threat for locally heavy snowfall in the Washington
Cascades. While there will be sufficient QPF throughout the Pacific
Northwest (>1,000 kg/m/s IVT today), the lack of a continental
polar air-mass is forcing heavier snowfall to accumulate above
4,000ft. Some lighter accumulations are possible around Stevens
Pass (1-3" through Sunday AM), most accumulating snowfall will
reside above pass level through Sunday AM. By Monday and into early
Tuesday, another Pacific storm system will approach the coast of
Oregon, but there remains a high degree of uncertainty as to how
far north the QPF reaches and how far inland it advances. At the
moment, WPC probabilities show low chances (10-30%) for snowfall
totals >4" on Monday. But cumulatively through this weekend and on
Monday, WPC probabilities show moderate-to-high chances (50-80%)
for snowfall >8" above 5,000ft. There were low-to-moderate chance
probabilities (30-50%) for snowfall >4" over the next few days at
Stevens Pass.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax


$$

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FOUS11 KWBC 011944
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Sat Nov 1 2025

Valid 00Z Sun Nov 02 2025 - 00Z Wed Nov 05 2025

...Washington Cascades...
Day 1...

An expansive trough extending from a deep/cold-core low centered
over the Gulf of Alaska continues to dominate the northeast Pacific
weather pattern through tonight. A shortwave trough rounding the
low is pushing into Vancouver Island this afternoon which will
cross Washington state through this evening and bring snow levels
down from 8000ft at present to around 3500ft which is at or below
most Washington Cascades pass levels. This occurs as continued
onshore flow maintains moderate precip rates on the western slopes
of the Cascades. 12Z HREF indicates mean snow rates of 1-2"/hr over
the higher Cascades between 06Z and 12Z tonight. Day 1 WPC snow
probabilities for >6" are 50-80% generally above the pass level.
Precip quickly tapers off Sunday morning as ridging builds in the
wave of the shortwave trough passage. A subsequent round of light
snow with snow levels of 3500-4000ft can be expected over the
Washington Cascades Monday night.


...Northern Rockies...
Day 3...

A shortwave trough pushes in from the OR coast Monday night along a
decent baroclinic zone over the Interior Northwest. Light to
moderate precip rates can be expected over the northern Rockies
with snow levels around 5000ft in the Bitterroots to 8000ft for the
Sawtooths in ID and around Yellowstone. Day 3 WPC snow
probabilities for >6" of 20-40% are limited to the higher portions
of this terrain.



The probability of significant ice across the CONUS is less than
10 percent.

Jackson



$$

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FOUS11 KWBC 020740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
240 AM EST Sun Nov 2 2025

Valid 12Z Sun Nov 02 2025 - 12Z Wed Nov 05 2025

...Northern Rockies...
Days 2-3...

A shortwave trough pushes in from the Pacific Northwest coast
Monday night and into Tuesday with a plume of modest 700-300mb
moisture and a band of weak 850-700mb WAA aloft. A lack of an
antecedent sub-freezing air-mass will keep snow confined to the
higher and more remote elevations of the northern Rockies. Snow
levels will vary by mountain range; from around 5000ft in the
Bitterroots and Lewis Range to 8000ft for the Sawtooths in ID, the
Absaroka, Tetons, and around Yellowstone. Days 2-3 WPC snow
probabilities are between 50-80% for >4" across most of these
ranges, while lower chances (10-30%) of >8" of snow are likely to
be confined to the higher terrain of the Cascades and Lewis Range.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax



$$

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FOUS11 KWBC 021833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
133 PM EST Sun Nov 2 2025

Valid 00Z Mon Nov 03 2025 - 00Z Thu Nov 06 2025

...Washington Cascades & Northern Rockies...
Days 1-2...

Active weather pattern picks up once again across the West as a
shortwave trough pushes in from the Pacific Northwest coast Monday
night and into Tuesday with a plume of modest 700-300mb moisture
and a band of weak 850-700mb WAA aloft. A lack of substantial
antecedent sub-freezing air- mass will keep heavy snow confined to
the higher and more remote elevations of the WA Cascades and
northern Rockies.However, accumulating snow is possible at some
passes above 4500ft. Snow levels will vary by mountain range; from
around 4000-5000ft in the WA Cascades, Bitterroots and Lewis Range
of NW MT to 8000ft for the Sawtooths in ID, the Absaroka, Tetons,
and around Yellowstone. QPF and snowfall amounts have increased
somewhat with today's forecast update across the Cascades. Days 1-2
WPC snow probabilities are now between 50-80% for >8" across the
WA Cascades above 5000ft, while lower chances (30-60%) of >8" of
snow are likely to be confined to the higher terrain of the NW MT
Ranges. The next system approaches the West Coast by Day 3, but is
associated with a much deeper eastern Pacific trough and in
response much higher snow levels along the West Coast, limiting
widespread impactful heavy snow.


The probability of significant ice across the CONUS is less than
10 percent.

Snell




$$

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FOUS11 KWBC 030732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
232 AM EST Mon Nov 3 2025

Valid 12Z Mon Nov 03 2025 - 12Z Thu Nov 06 2025

...Washington Cascades & Northern Rockies...
Days 1-3...

An active weather pattern resumes across the West as a shortwave
trough pushes in from the Pacific Northwest coast Monday night and
into Tuesday with a plume of modest 700-300mb moisture and a band
of weak 850-700mb WAA aloft. A lack of substantial antecedent sub-
freezing air-mass will keep heavy snow confined to the higher and
more remote elevations of the WA Cascades and northern Rockies.
However, accumulating snow is possible at some passes above 4500ft,
especially Stevens Pass in the WA Cascades. Snow levels will vary
by mountain range; from around 4000-5000ft in the WA Cascades,
Bitterroots and Lewis Range of NW MT to 8000ft for the Sawtooths in
ID, the Absaroka, Tetons, and around Yellowstone. Days 1-2 WPC
snow probabilities range between 50-80% for >8" across the WA
Cascades above 5000ft, while lower chances (30-60%) of >8" of snow
are likely to be confined to the higher terrain of the NW MT
Ranges.

As some residual light mountain snow persists on Tuesday, the
next system approaches the West Coast Tuesday night with a
moderate-to-strong atmospheric river directing an impressive plume
of moisture within strong 850-500mb WAA into the Northwest U.S
through Wednesday.. Aside from the taller peaks of the WA/OR
Cascades and Northern California's mountain peaks, most snowfall
will reside above 5,000ft in elevation. Precipitation is likely to
spill over into the northern Rockies late Wednesday and into
Thursday morning with some accumulating snowfall in the Sawtooth,
Blue, Tetons, Bitterroot, and Lewis Ranges. The Sawtooth are the
only notable mountains that WPC probabilities shows having moderate
chances (40-60%) for snowfall totals >4" above 7,000ft.

...Northern New England Appalachians...
Days 1 & 3...

A pair of storm systems will traverse New England; one on Monday
and the other on Wednesday, will generate periods of snow in a
couple different fashions. Today, snowfall will largely be
generated via 850-700mb CAA and WNWrly upslope flow into the
northern Appalachians. Despite the CAA at low-levels, boundary
layer temperatures remain generally above freezing with the
exception of the peaks of the Adirondacks and White Mountains. WPC probabilities show moderate chances (10-30%) for snowfall totals

4" in these mountain ranges peaks, which includes most notably

Mount Washington.

By Wednesday, an amplifying shortwave trough exiting the Great
Lakes will generate healthy upper-level ascent over New England
that prompts the development of a low pressure system. This
developing storm system is a progressive one, but a modest plume
of moisture accompanying the storm gives rise to periods of snow
Wednesday night and into Thursday morning. The heaviest snowfall
likely occurs as the storms tracks over coastal Maine and strong
CAA and upslope NWrly flow envelops the Adirondacks, Green, and
White Mountains. Snow levels will drop more this go round compared
to Monday, dropping as low as 1,000ft from the Green Mountains on
north and east through western Maine. WPC probabilities show
moderate chances (40-60%) for snowfall >4" in parts of the Great
North Woods of northern New Hampshire and over western Maine. Mount
Washington is most likely to be the favorite to see the heaviest
snowfall, with low-to-moderate chances (20-40%) for snowfall totals

8" at Mount Washington's summit. Some hazardous travel conditions

on roadways are possible in the peaks of the Adirondacks and White
Mountain passes late Wednesday night into Thursday morning. Note
the forecast still has a high degree of uncertainty and a change in
forecast track and or intensity could result in changes in the
snowfall forecast.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax







$$

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FOUS11 KWBC 031948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Mon Nov 3 2025

Valid 00Z Tue Nov 04 2025 - 00Z Fri Nov 07 2025

...Pacific Northwest through the Central Rockies...
Days 1-3...

An active pattern begins tonight across the Northwest and
eventually spilling into the Intermountain west, as a series of
three distinct impulses moving eastward across the region.

The first of these will lift onshore near OR early tonight, with a
weakening surface wave also pushing northeast beneath it. This will
channel modest moisture onshore, and as the system progressively
pushes east, a stripe of light to moderate precipitation will occur
from the WA/OR coast through the Northern Rockies. In general
snowfall will accumulate above 4000-5000 ft, but total
accumulations are expected to be modest as reflected by WPC
probabilities for 4+ inches that are above 70% only in the highest
terrain near Mt. Rainier as well as across the Lewis Range in the
Northern Rockies.

A stationary front wavering across the area will serve initially
as the demarcation between higher snow levels to the south and
lower to the north, but this boundary will begin to push north as a
warm front D2. This evolution will be driven by an impressively
amplifying trough over the eastern Pacific downstream of a closed
low which will lift into northern British Columbia Thursday.
Strongly confluent and southerly flow ahead of this feature will
surge impressive IVT into the Pacific Northwest, reflective of a
strong atmospheric river which will peak in intensity on D2. This
impressive IVT (>90% chance of exceeding 750 kg/m/s) will reignite precipitation across the area while concurrently driving snow
levels to 7000-8000 ft. This should preclude considerable impacts
from snow at any of the passes, but heavy snow is likely in the
highest terrain from Mt. Shasta northward along the Cascades where
WPC probabilities for 6+ inches are above 70%.

Finally during D3, precipitation associated with this AR will spill
eastward, reaching the Northern and Central Rockies as far as
Wyoming, while a tertiary impulse moves into the Pacific Northwest
once again with renewed heavy precipitation. Snow levels will fall
gradually behind the impulse on D2, but remain somewhat elevated at
around 5000-6000 ft D3. WPC probabilities for more than 4 inches of
snow accumulation extend from the WA Cascades through the
Sawtooth/Salmon River ranges of ID and into the region around
Yellowstone NP where they peak at 70-90%.


...Northern New England and the Adirondacks...
Day 1...

A low pressure system moving well east of New England will interact
with a shortwave racing southeast out of Ontario to draw moisture
back into New England tonight. While the duration of available
moisture will be limited due to rapid drying behind the cold front
accompanying the aforementioned shortwave, upslope flow during a
period of CAA will result in periods of moderate to heavy snow,
especially in the Presidential Range of NH, with additional light
accumulations across the Adirondacks. WPC probabilities for 4+
inches of snow are as high as 10% in the Adirondacks, but above 80%
near Mt. Washington where locally 8-10 inches of snow is likely.

Day 3...

A clipper type low pressure will race southeast out of Ontario
beginning late Thursday, crossing northern New England while
amplifying through Friday morning. The system will be progressive
and exit the Maine coast by 12Z Thursday, but moisture will persist
behind the low as an impressive TROWAL pivots cyclonically around
the rapidly deepening system. Initially, precipitation will be all
rain as snow levels are elevated and WAA prevents any cooling.
However, as the low departs, rapid cooling is likely both through
isallobaric flow into the strengthening system, but also aided by
impressive CAA in its wake. This will result in a crash of snow
levels from around 3000 ft early D3 to as low as 500-1000 ft by 12Z
Thursday before precipitation wanes Thursday aftn. The lowering
snow levels combined with impressive ascent through the TROWAL and
in response to increasing upslope on veering N/NW winds will help
snowfall accumulate in the terrain of Northern New England on
Thursday. The heaviest snow is expected near Mt. Washington and
across the interior mountains of northern Maine where WPC
probabilities are 30-50% for 4+ inches of snow.



The probability of significant ice across the CONUS is less than
10 percent.


Weiss


$$

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FOUS11 KWBC 040832
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Tue Nov 4 2025

Valid 12Z Tue Nov 04 2025 - 12Z Fri Nov 07 2025

...Pacific Northwest through the Central Rockies...
Days 1-3...

An active pattern, driven by an impressive northeast Pacific
longwave trough, will deliver a steady diet of rich Pacific
moisture into the Pacific Northwest and Northern Rockies. ECMWF
SATs for 06Z Wednesday show 1000-700mb heights that are below the
0.5 climatological percentile and a strong atmospheric river that
is headlined by a >1,250 kg/m/s IVT. Even as this atmospheric river
(AR) wains Wednesday evening and another moderate AR arrives on
Thursday, from a winter perspective, the strong 850-500mb WAA and a
lack of sufficiently cold air-masses will keep accumulating
snowfall limited to the more remote areas of the Cascades and
Northern Rockies. While some lingering Pacific moisture streaming
across these mountain ranges on Day 1, the ARs on Days 2 and 3 will
produce the bulk of the heavy mountain snow. Cumulatively over the
next 3 days, WPC probabilities >50% for snowfall >8" are most
commonly seen above 5,000ft in the WA Cascades, above 7,000ft in
the Sawtooth and Lewis Ranges, and above 9,000t in the Absaroka,
Tetons, and Wind River Ranges. Passes not yet closed for the
season in these ranges could contend with hazardous travel
conditions.


...Northern New England and the Adirondacks...
Day 2...

By Wednesday morning, an amplifying upper level trough over the
Great Lakes will deepen a wave of low pressure tracking through
southern Ontario Wednesday afternoon, culminating in a potent sub-990mb
low over the Gulf of Maine early Thursday morning. Precipitation
will overtake much of northern NY and northern New England by
Wednesday evening first via 850-700mb FGEN and associated WAA
within that atmospheric layer. Given the lack of a sufficiently
cold antecedent air-mass, any periods of snow will likely be
confined to the tallest peaks of the Adirondacks, Green and White
Mountains, and western Maine. It is not until the storm heads for
coastal Maine, when low-level CAA ensues and NWrly flow increase
favorable upslope ascent into these mountain ranges that leads to
snow levels plummeting to as low as 500-1,000ft throughout northern
NY and northern New England. It is a fast moving storm system, and
the time roughly between 03-09Z Thursday is when the heaviest
snowfall rates are likely to occur. No long after 12Z Thursday,
only lingering upslope flow into the >2,000ft ranges of the
Adirondacks, Green, and White Mountains are likely to see any
lingering snowfall.

WPC probabilities shows moderate-to-high chances (40-70%) for
snowfall >4" in western ME, northern NH, and the White Mountains
(including most notably Mount Washington). The peaks of the Green
Mountains and Adirondacks generally have low chances (10-30%) for
totals >4", with their tallest peaks having the best chances for

4" totals. Impacts, such as snow-covered roads and reduced

visibility, will generally be confined to more remote locations of
these areas.


The probability of significant ice across the CONUS is less than
10 percent.


Mullinax


$$

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FOUS11 KWBC 042007
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
307 PM EST Tue Nov 4 2025

Valid 00Z Wed Nov 05 2025 - 00Z Sat Nov 08 2025

...Pacific Northwest through the Central Rockies...
Days 1-3...

An active pattern across the Pacific will continue through the week
as a closed low lifts slowly into British Columbia, leaving
persistently confluent W/SW flow across the Pacific and channeled
into the West Coast. This will result in an extend period of
impressive moisture advection and IVT surging onshore, and
probabilities for a strong atmospheric river (AR) moving onto the
coast exceed 80% from both the GEFS and ECENS ensemble systems on
D1. The intensity of this moist advection is additionally reflected
by NAEFS IVT percentiles that exceed the 99.5 percentile across CA
Wednesday afternoon.

This suggests an impressive precipitation plume will push from
CA/OR northeast Wednesday aftn through Thursday aftn, with
precipitation spillover reaching as far as the Northern and Central
Rockies. However, most of this precipitation will fall as rain as
the accompanying WAA surges snow levels to 7000-8000 ft, keeping
any snow well above pass levels through Thursday. A secondary surge
of precipitation associated with another impulses embedded within
the confluent onshore flow will lower snow levels at least subtly,
to around 5000 ft, with additional heavy precipitation. At this
time, impactful snow will likely occur at some of the higher
passes, especially Washington Pass in the WA Cascades before Friday
morning, before this final impulse shifts east causing precip to
wind down across the Cascades but continue, in lighter fashion
across the Northern and Central Rockies.

WPC probabilities D1 are moderate (50-70%) for more than 6 inches
of snow in the higher Sierra and northern WA Cascades, before
expanding and shifting east into Salmon River/Sawtooth ranges, the
Tetons, and Northern Rockies, while at the same time continuing
across the northern WA Cascades. On D3 the heaviest snow is
expected across the WA Cascades where WPC probabilities reach above
70% for 8+ inches above 5000 ft, with moderate probabilities
(30-50%) for 6+ inches continuing across portions of the Northern
Rockies and higher elevations of ID and NW WY.


...Northern New England and the Adirondacks...
Day 2...

A rapidly intensifying clipper-type low pressure will move
progressively E/SE from Ontario, Canada, across New England, and
then out to sea south of the Canadian Maritimes by 00Z/Friday. This
low will spread significant moisture eastward on robust low-level
fgen leading to modest TROWAL development pivoting across Northern
New England. While the accompanying WAA will help spread
significant moisture into the area, it will also drive snow levels
to 4000-5000 ft, suggesting that except for the highest peaks of
northwest Maine, the pre-low precipitation will be all in the form
of rain. However, as the low kicks east, rapid cold advection in
its wake, aided by impressive isallobaric flow into the deepening
system, will cool the column dramatically, reflected by snow levels
falling to 500-1000 ft by 12Z Thursday. This cooling column
combined with increasing upslope flow into the terrain on the NW
flow will result in a period of moderate to heavy snowfall in the
higher terrain, with light snow gradually spreading into the lower
elevations of VT/NH/ME and Upstate NY before the DGZ dries and
precipitation wanes Thursday aftn.

The heaviest snow is likely above 2000 ft in the Adirondacks and
Whites, although some moderate accumulations are also likely in the
highest Greens. This is reflected by WPC probabilities which
indicate a moderate risk (50-70% chance) for more than 4 inches of
snow, with locally as much 8 inches in the highest Presidential
Range peaks. Light accumulations of a dusting or more are likely
elsewhere from Lake Ontario through central Maine, except across
the Champlain Valley, resulting in the first notable snow of the
year in some of the lower elevations of northern New England.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss


$$

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FOUS11 KWBC 050755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Wed Nov 5 2025

Valid 12Z Wed Nov 05 2025 - 12Z Sat Nov 08 2025

...Pacific Northwest through the Central Rockies...
Days 1-3...

An active pattern across the Pacific will continue through the week
as a closed low lifts slowly into British Columbia, leaving
persistently confluent W/SW flow across the Pacific and channeled
into the West Coast. This fosters an extend period of impressive
moisture advection and IVT surging onshore, and probabilities for a
strong atmospheric river (AR) moving onto the coast exceed 80%
from both the GEFS and ECENS ensemble systems on D1. The intensity
of this moist advection is additionally reflected by NAEFS IVT
percentiles that exceed the 99.5 percentile across CA Wednesday
afternoon.

This suggests an impressive precipitation plume will push from
CA/OR northeast Wednesday aftn through Thursday aftn, with
precipitation spillover reaching as far as the Northern and Central
Rockies. However, most of this precipitation will fall as rain as
the accompanying WAA surges snow levels to 7000-8000 ft, keeping
any snow well above pass levels through Thursday. A secondary surge
of precipitation associated with another disturbance embedded
within the confluent onshore flow will lower snow levels at least
slightly, to around 5000 ft, with additional heavy precipitation.
At this time, impactful snow will likely occur at some of the
higher passes, especially Washington Pass in the WA Cascades before
Friday morning, before a final impulse shifts east causing precip
to wind down across the Cascades but continue, in lighter fashion,
across the Northern and Central Rockies.

WPC probabilities D1 are moderate (50-70%) for >6" inches of snow
in the northern WA Cascades, before expanding and shifting east
into Salmon River/Sawtooth ranges, the Tetons, and Northern
Rockies, while at the same time continuing across the northern WA
Cascades. On D2 and bleeding into D3, the heaviest snow is
expected across the WA Cascades where WPC probabilities reach above
70% for 8+ inches above 5000 ft, with moderate probabilities
(30-50%) for 6+ inches continuing across portions of the Northern
Rockies and higher elevations of ID and NW WY. Cumulatively through
Friday night, 3-day snowfall probabilities show some moderate
chances (40-60%) for snowfall totals to eclipse 12" in the tallest
reaches of the northern WA Cascades, the Sawtooth, and Tetons.


...Northern New England and the Adirondacks...
Day 1...

A rapidly intensifying clipper-type low pressure will move
progressively E/SE from Ontario, across New England, and then out
to sea south of the Canadian Maritimes by Thursday afternoon. This
low will spread significant moisture eastward on robust low-level
FGEN leading to a pronounced TROWAL pivoting across Northern New
England. The accompanying WAA will help spread significant
moisture into the area, but the WAA will also drive snow levels up to
4000-5000 ft, suggesting that except for the highest peaks of
northwest Maine, the pre-low precipitation will be all in the form
of rain Wednesday afternoon. However, as the low tracks towards the
New England coast, rapid CAA in its wake, aided by impressive
isallobaric flow into the deepening system and topographically-
enhanced upslope flow, will cool the column dramatically,
reflected by snow levels falling to 500-1000 ft by 12Z Thursday.
This results in a period of moderate to heavy snowfall in the
higher terrain, with light snow gradually spreading into the lower
elevations of VT/NH/ME and Upstate NY before the DGZ dries and
precipitation dissipates Thursday afternoon.

The heaviest snowfall is likely to unfold above 2000ft in the
Adirondacks and Whites, although some moderate accumulations are
also likely in the highest Greens. This is reflected by WPC
probabilities which indicate a moderate risk (50-70% chance) for
more than 4 inches of snow, with locally as much 8 inches in the
highest Presidential Range peaks. Light accumulations of a dusting
or more are likely elsewhere from Lake Ontario through central
Maine, except across the Champlain Valley, resulting in the first
notable snow of the year in some of the lower elevations of
northern New England.


The probability of significant ice across the CONUS is less than
10 percent.


Mullinax/Weiss




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FOUS11 KWBC 052051
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 PM EST Wed Nov 5 2025

Valid 00Z Thu Nov 06 2025 - 00Z Sun Nov 09 2025

...Pacific Northwest through the Central Rockies...
Days 1-3...

At the start of the forecast period, a remnant atmospheric river
plume will continue to migrate inland, spreading precipitation into
the Northern and Central Rockies late tonight and Thursday. The
mild nature of the eastern Pacific airmass spilling into the West
will maintain high snow levels around 7000-8000 ft with this
initial round, above pass levels. By tomorrow afternoon, another
compact closed low is forecast to pivot around the offshore mean
trough and usher in another atmospheric river, albiet weaker. While
WAA associated with this activity will result in gradually rising
snow levels throughout Thursday, impactful mountain snowfall is
still expected across the higher mountain passes in the Northern
Washington Cascades Thursday night into Friday. Eventually, a
shortwave translating eastward will once again shift mountain
snowfall chances into the Northern and Central Rockies. WPC
probabilities on D1 and bleeding into D2 depict a high likelihood
of 12+ inches (75-90%) of snowfall in the peaks of the northern
Washington Cascades. As the activity shifts eastward, 60-90%
probabilities of exceeding 6 inches are noted in the higher
elevations of the Wyoming Tetons.

...Northern Plains and the Upper Midwest...
Day 3...

Emerging clipper system is forecast to eject across the Northern
Plains as the aforementioned Rockies shortwave phases with a
disturbance in the Canadian Prairies. By Saturday, modest
frontogenetic snowfall is expected to develop along the northwest
flank of the surface low center as it dives southeastward across
the Northern Plains and Upper Midwest. Overall accumulations should
be quite low with this event (WPC probabilities of 1" are around
50%), but locally hazardous travel conditions could materialize
owing to strong gradient winds on the periphery of the low and some
areas experiencing their first snow of the season.

...Northern New England and the Adirondacks...
Day 1...

Forecast reasoning remains unchanged as a rapidly intensifying
clipper-type low pressure will move progressively E/SE from
Ontario, across New England, and then out to sea south of the
Canadian Maritimes by Thursday afternoon. This low will spread
significant moisture eastward on robust low- level FGEN leading to
a pronounced TROWAL pivoting across Northern New England. The
accompanying WAA will help spread significant moisture into the
area, but the WAA will also drive snow levels up to 4000-5000 ft,
suggesting that except for the highest peaks of northwest Maine,
the pre-low precipitation will be all in the form of rain Wednesday
afternoon. However, as the low tracks towards the New England
coast, rapid CAA in its wake, aided by impressive isallobaric flow
into the deepening system and topographically- enhanced upslope
flow, will cool the column dramatically, reflected by snow levels
falling to 500-1000 ft by 12Z Thursday. This results in a period of
moderate to heavy snowfall in the higher terrain, with light snow
gradually spreading into the lower elevations of VT/NH/ME and
Upstate NY before the DGZ dries and precipitation dissipates
Thursday afternoon.

The heaviest snowfall is likely to unfold above 2000ft in the
Adirondacks and Whites, although some moderate accumulations are
also likely in the highest Greens. This is reflected by WPC
probabilities which still indicate a moderate risk (50-70% chance)
for more than 4 inches of snow, with locally as much 8 inches in
the highest Presidential Range peaks. Light accumulations of a
dusting or more are likely elsewhere from Lake Ontario through
central Maine, except across the Champlain Valley, resulting in the
first notable snow of the year in some of the lower elevations of
northern New England.


The probability of significant ice across the CONUS is less than
10 percent.


Asherman/Mullinax







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FOUS11 KWBC 060759
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Thu Nov 6 2025

Valid 12Z Thu Nov 06 2025 - 12Z Sun Nov 09 2025

...Pacific Northwest through the Northern Rockies...
Days 1-2...

The next shortwave trough passage over the Pacific Northwest is
this evening as a potent wave crosses Washington, reaching mid
Montana Friday morning. Warm/moist advection ahead of the wave
raises snow levels on the Washington Cascades from 5000ft to
6500ft through this afternoon before sharply dropping to 4000ft
overnight as precip rates slowly subside post axis passage. Day 1
WPC snow probabilities for >6" are 40-80% generally above the
higher WA Cascade road passes.

Pacific moisture surges inland over the northern Rockies tonight
into Friday. However, snow levels rise only to around 6000ft
tonight before dropping to around 4500ft under the trough on
Friday. Day 1.5 WPC snow probabilities for >6" are generally
30-60% over the higher terrain of the Salmon River Mtns of ID, the
Bitterroots, and the Lewis Range of Glacier NP and 50-80% for the
Tetons.


...Northern Plains to Great Lakes...
Days 2-3...

Potent shortwave trough from the Pacific pivots from an eastward
trajectory to southeasterly Friday night over eastern Montana. This
trough then swings through Iowa later Saturday before being
reinforced over the Great Lakes Saturday night by a Canadian
trough dropping south. By Saturday morning, modest frontogenetic
snowfall is expected to develop near the MT/ND border which is
along the northwest flank of the surface low center. This wave is
fairly progressive and working with marginal thermals. Day 2.5 WPC probabilities for >2" are 10-50% in a stripe across ND. The
reinforcing trough could aid some more notable snow banding along
the IA/MN border and trigger some lake enhanced snow, including
over central MI where Day 3 snow probs for >4" are around 30%.
Locally hazardous travel conditions could materialize owing to
strong gradient winds on the periphery of the low and some areas
experiencing their first snow of the season.


The probability of significant ice across the CONUS is less than
10 percent.


Jackson



$$

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FOUS11 KWBC 062059
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EST Thu Nov 6 2025

Valid 00Z Fri Nov 07 2025 - 00Z Mon Nov 10 2025

...Pacific Northwest through the Northern Rockies...
Day 1...

The last shortwave in this series which has produced consistent
active weather across the region will cross into Washington State
early D1 before translating quickly eastward into the Northern
Rockies by 00Z/Saturday. This shortwave will be accompanied by a
pronounced zonal jet streak racing across the Pacific such that
there will be a favorable overlap of height falls/PVA and left-exit
diffluence to drive significant ascent. Downstream of this
impulse, low-to-mid level southwest flow will transport copious
moisture northeast as an atmospheric river (AR) characterized by
high probabilities (>90% chance) of IVT exceeding 250 kg/m/s from
both the GEFS and ECENS ensemble systems. While this will help
produce a stripe of significant precipitation from the Pacific
Northwest through the Northern Rockies, the overall speed of the
system will somewhat limit the total amount of precipitation during
D1.

Additionally, snow levels within the core of the AR, due to the
accompanying WAA, will rise to 6000-7000 ft, but will crash behind
the associated surface cold front (and beneath the core of the
upper low) to reach as low as 3500 ft across the Cascades and into
the interior Northwest. This will allow for significant snowfall
accumulations to reach to pass level, especially at Washington and
Stevens Passes in the Cascades, where the most significant impacts
to transportation are likely.

WPC probabilities indicate a high risk (>70%) for more than 6
inches of accumulation across the northern WA Cascades, including
Washington Pass, and also extend into portions of the Northern
Rockies and in the vicinity of the Tetons.


...Northern Plains through the Great Lakes...
Days 2-3...

...Strengthening Clipper from North Dakota to Michigan...
A potent shortwave digging from Alberta, Canada will dive southeast
into the Northern Plains Friday night and then continue to
traverse rapidly southeast, reaching the Upper Midwest late
Saturday night. This feature will initially be of minimal intensity
producing modest height falls/PVA, but will steadily deepen with
time as it becomes more deeply embedded in its parent trough. By
Saturday night, the accompanying upper level jet streak will begin
to arc more poleward, producing more favorable curvature to result
in strong left-exit diffluence, which will overlap with the most
significant height falls/PVA across lower Michigan to cause
intensification of the surface low. This will occur late Saturday
night before the entire system exits into Ontario by Sunday.

While this feature will be progressive, it will likely create the
first notable snowfall of the season in a stripe arcing from North
Dakota through Iowa and into lower Michigan. Examination of
regional soundings indicates that forcing for ascent will be
somewhat modest through 00Z Sunday (end of D2) before become more
intense thanks to impressive 925-700mb fgen on WAA on D3. The DGZ
appears subjectively elevated so snow growth will be limited, but
should still accumulate lightly as reflected by WPC probabilities
for 1+ inches of 10-50% aligned from central ND through northern
IA. Although this snowfall is not exceptional, it will be impactful
as it likely to be the first accumulating snowfall of the season
for this region.

During D3, however, forcing intensifies, especially across lower
Michigan where mesoscale analysis indicates a moderate threat for
CSI due to impressive fgen overlapping the DGZ and driving ascent
into a region of theta-e lapse rates of 0C/km. The SREF 3-hr
snowfall probabilities indicate the potential for 2-3" during this
time, and 1"/hr snowfall appears reasonable during this period of
most intense lift. Despite the rapid progression of the wave, this
could result in more than 4 inches of snow, especially across lower
Michigan in the vicinity of Detroit, where WPC probabilities for
more than 4 inches of snow reach 10-30%.

...Lake Effect Snow beginning Sunday...

A strong vort max digging southward from Ontario, Canada into the
Great Lakes will help carve out a deepening and amplifying
mid/upper level trough across much of the eastern U.S. starting on
Sunday. Strong CAA underneath this vort max/trough and in the wake
of a strengthening surface low tracking northeast into
Ontario/Quebec will deliver a notably colder, winter-like air mass
to the region, headlined by 850mb temperatures between 10 and 15
degrees below 0C. This injection of unseasonably cold air (near or
below the 10th climatological percentile) over top the warm Great
Lakes (temperatures of +10 to +15C) will result in an impressive
convective environment with model soundings revealing steep lapse
rates and deep mixing heights to near or above 700mb. Given delta
Ts of 20 to 30C, the environment appears more than supportive of
lake effect snow production.

Lake parallel north-northwest to northerly surface winds along
with increasingly unidirectional winds aloft will act on the
impressive instability highlighted above. Combined, this will
support the development of a few prominent north-south lake effect
snow bands, particularly downwind of Lake Superior and Lake
Michigan during the D3/Sunday period. These snow bands will
primarily be focused across portions of the U.P of Michigan, where
the heaviest snowfall may exceed (50% chance) 4 inches. Additional
lake effect snowfall is expected along and just inland of the
eastern lake shore of Lake Michigan, and across northern Indiana,
where WPC probabilities for 2+ inches are as high as 30%.
Additionally heavy lake effect snow is expected beyond this
forecast period into D4 as well.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss/Miller






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FOUS11 KWBC 070841
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 AM EST Fri Nov 7 2025

Valid 12Z Fri Nov 07 2025 - 12Z Mon Nov 10 2025

...Washington Cascades through the Northern Rockies...
Day 1...

Upper low over Washington State early this morning will shift east
to central MT by midday on a strong westerly jet. Snow levels drop
to around 4000ft under the low with precip rates decreasing in the
wake. Day 1 snow probabilities for >6" additional after 12Z are
50-80% for the highest WA Cascades, ranges in and south of Glacier
NP, and the Tetons to the Wind River Range.


...Northern Plains through the Interior Northeast...
Days 1-3...

...Strengthening low from North Dakota to the Northeast...
A potent shortwave pivots southeast from eastern Montana
this evening and digs to Iowa through Saturday. A reinforcing
trough dives south over the Upper Midwest Saturday night before
developing into a deep low over the Great Lakes Sunday night. The
surface low rapidly develops over the eastern Great Lakes Saturday
night downstream of the reinforcing trough. The low then mainly
tracks along/north of the St. Lawrence in eastern Canada.

While this feature is progressive over the northern Plains, it
will create a stripe of snowfall across ND (where Day 1.5 snow
probabilities for >2" are 30-50%) with lesser amounts over eastern
SD, down along the MN/IA border. However, forcing intensifies
across lower Michigan where mesoscale analysis indicates a moderate
threat for CSI due to impressive fgen overlapping the DGZ and
driving ascent into a region of theta-e lapse rates of 0C/km
Saturday night. Day 2.5 snow probabilities for >2" are 30-50% over
central lower Michigan.


...Lake Effect Snow beginning Sunday...
The deepening and amplifying mid/upper level trough over the
central Great Lakes Sunday that develops into a deep low Sunday
night will bring Strong CAA and a winter-like air mass to the
region, headlined by 850mb temperatures between negative 10 and 15
degrees C. This injection of unseasonably cold air (near or below
the 10th climatological percentile) over top the warm Great Lakes
(temperatures of +10 to +15C) will result in an impressive
convective environment with model soundings revealing steep lapse
rates and deep mixing heights to near or above 700mb. Given delta
Ts of 20 to 30C, the environment appears more than supportive of
lake effect/enhanced snow production.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior Sunday and Lake
Michigan Sunday night. The U.P of Michigan bands will be rather
stable which leads to Day 3 WPC probabilities for >6" in the
60-90% range east of the Keweenaw Peninsula and around 30% for the
Porcupine Mtns. There is increasing confidence on Sunday night into
Monday snow banding from Lake Michigan over northern Indiana where
Day 3 snow probabilities for >6" are now 40-60%. This area, along
with downstream snow banding from Lake Erie will need to continue
to be monitored for the heavy snow banding threat.


The probability of significant ice across the CONUS is less than
10 percent.


Jackson


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FOUS11 KWBC 072106
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EST Fri Nov 7 2025

Valid 00Z Sat Nov 08 2025 - 00Z Tue Nov 11 2025

...Northern Plains through the Interior Northeast...
Days 1-3...

...Strengthening low from North Dakota to the Northeast...
A potent shortwave pivots southeast from eastern Montana
this evening and digs to Iowa through Saturday, producing the first accumulating snow of the season for some locations in the Midwest
and Great Lakes. A reinforcing trough then dives south over the
Upper Midwest Saturday night before developing into a deep low over
the Great Lakes Sunday night. The surface low rapidly develops
over the eastern Great Lakes Saturday night downstream of the
reinforcing trough and mainly tracks along/north of the St.
Lawrence in eastern Canada Sunday.

While this feature is progressive over the northern Plains, it
will create a stripe of snowfall on the northern/northwestern
periphery of the low pressure system. This includes a swath from
ND (where Day 1 NBM snow probabilities for >2" are around 25%)
with lesser amounts over eastern SD, down through IA, the WI/IL
border region and further into the Lower Great Lakes. However,
forcing intensifies by the time it reaches IA and as it crosses
into the Lower Great Lakes Saturday afternoon and evening across
lower Michigan, where mesoscale analysis indicates a moderate
threat for CSI due to impressive fgen overlapping the DGZ and
driving ascent into a region of theta-e lapse rates of 0C/km
Saturday night. This may lead to snowfall rates exceeding
0.5-1.0"/hr at times, as depicted by the HREF snowband probability
tracker. Day 2 NBM snow probabilities for >2" are 20-30% over
central lower Michigan.


...Lake Effect Snow beginning Sunday...
The deepening and amplifying mid/upper level trough over the
central Great Lakes Sunday that develops into a deep low Sunday
night will bring Strong CAA and a winter-like air mass to the
region, headlined by 850mb temperatures between negative 10 and 15
degrees C. This injection of unseasonably cold air (near or below
the 10th climatological percentile) over top the warm Great Lakes
(temperatures of +10 to +15C) will result in an impressive
convective environment with model soundings revealing steep lapse
rates and deep mixing heights to near or above 700mb. Given lake
temp and 850mb air temp delta Ts of 20 to 30C, the environment
appears more than supportive of lake effect/enhanced snow
production.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior Sunday and Lake
Michigan Sunday night into Monday. Day 2 NBM probabilities for >4"
are 40-80% across portions of the U.P. of Michigan and the far NW
corner of lower Michigan. There is increasing confidence for
enhanced banded snow aided by a potent vort max and a potential
lake induced mesolow Sunday night into Monday morning over parts
of northeast Illinois (including the Chicago metro) and northern
Indiana. Day 3 NBM probabilities for >4" are 40-80% with
probabilities for >6" 30-70%. This area, along with downstream
snow banding from Lake Erie will need to continue to be monitored
for the heavy snow banding threat given the potential for early
season impacts.

Cold upslope northwesterly flow will also lead to increasing snow
potential across parts of the Appalachians on Day 3/Monday, with
NBM probabilities highlighting probabilities for >4" of 25-50%.


The probability of significant ice across the CONUS is less than
10 percent.


Snell/Miller





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FOUS11 KWBC 080907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 AM EST Sat Nov 8 2025

Valid 12Z Sat Nov 08 2025 - 12Z Tue Nov 11 2025

...Strong and deep low develops over the Great Lakes Sunday with
notable Lake Effect Snow through Tuesday...


...North-Central Plains to southern Michigan...
Day 1...

Shortwave trough/vort max over eastern MT early this morning swings
southeast to southern Iowa today and Ohio tonight. Ongoing snow
banding over the Dakotas ahead of this wave shifts southeast
through western Iowa this morning where marginal thermals should be
overcome in the better banding to allow accumulations. Day 1 WPC
probabilities for >4" are around 10 percent in west-central IA.
Forcing intensifies over the Midwest late tonight into Saturday.
There is a moderate threat for CSI banding along the southern MI
border due to fgen overlapping the DGZ and driving ascent into a
region of theta-e lapse rates of 0C/km. This may lead to snowfall
rates of 1.0"/hr at times per the 00Z HREF. Day 1.5 snow
probabilities for >4" snow are 30-60% over northern IN and southern
MI up to the Detroit metro as well as far northwest OH.


...Lake Effect/Enhanced Snow tonight through Tuesday...
A reinforcing shortwave trough rounding a deep low shifting south
from Hudson Bay crosses the Upper Midwest tonight with a deep
second lobe developing over Michigan Sunday that swings south
before tracking over the Interior Northeast Monday night. The
surface low rapidly develops over Ohio tonight downstream of the
initial shortwave trough. The reinforcing trough importantly slows
the progress of the surface trough along the Northeast coast Sunday
which prolongs the following flow over the Great Lakes for lake
effect/enhanced snow tonight of Lake Superior shifting through all
the Great Lakes before easing off Lake Ontario on Tuesday.
Strong CAA brings a winter-like airmass to the region, headlined
by 850mb temperatures between negative 10 and 12 degrees C. This
cold air (near or below the 10th climatological percentile) over
the warm Great Lakes (temperatures of +10 to +15C) will result in
an impressive convective environment with model soundings
indicating steep lapse rates and deep mixing heights to near or
above 700mb. Given lake temp and 850mb air temp delta Ts of 20 to
30C, the environment will be rather supportive for lake
effect/enhanced snow production.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior tonight through
Monday, Lake Michigan Sunday night through Monday, Lakes Huron and
Erie Sunday night through Monday night, and Lake Ontario Monday
night/Tuesday.
Day 2 WPC probabilities for >6" are over 80% in the Huron Mtns of
the U.P. of MI and up to 40% in the Porcupine Mtns while 40-80% for
portions of the western L.P. shoreline and all of the Indiana
shoreline. Day 3 WPC probabilities for >6" are 60% over Northern
Indiana for continued banding threats (most notably in the 00Z
experimental RRFS), around 80% near Port Huron, MI (the exact wind
direction will determine which side of the border gets hit worst), 40-80%
south of Lake Erie east of Cleveland, and around 10% in the Tug
Hill.

Cold upslope northwesterly flow and a moist fetch from Lake
Michigan will also cause upslope snow showers for the Central
Appalachians Sunday night through Monday night with Day 3 WPC
probabilities for >6" 40-70%.



Jackson


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FOUS11 KWBC 081953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 PM EST Sat Nov 8 2025

Valid 00Z Sun Nov 09 2025 - 00Z Wed Nov 12 2025

...Great Lakes, Northeast, and central/southern Appalachians...
Days 1-3...

Shortwave trough/vort max near western IA this afternoon is
expected to swings east across the Midwest tonight and into the
Lower Great Lakes by Sunday as it begins to turn northeast around a
deeper upper low centered over southern Ontario. Ongoing snow
banding over central/northern IA ahead of this wave also shifts
east on the northern periphery of a surface low. Marginal surface
temperatures should limit snowfall somewhat outside of more intense
snow bands and rates approaching 1"/hr. These rates and light
accumulations become more likely by Sunday morning across northern
IN, northwest OH, and southern MI as fgen increases and overlaps
the DGZ. This is highlighted nicely within the 12z HREF. Day 1 WPC probabilities for >4" are around 20-30% from northern IN to
southern MI and northwest OH. Additionally, WAA ahead of this
deepening low across northern New England and Upstate NY will
overspread precipitation into subfreezing surface temperatures,
leading to some mixed ptype concerns. Snowfall amounts should
remain mostly light and most likely to occur after the system has
exited the region on Mon-Tues morning. However, some light freezing
rain could be possible across northern NY, including the
Adirondacks and favorable low elevations along the St. Lawrence
where low-level cold air may remain locked in place on the
northwest side of the low system. WPC probabilities for at least
0.1" of ice accretion are between 10-40% and also include the White
Mts of NH and ME.


...Lake Effect/Enhanced Snow tonight through Tuesday...
A reinforcing shortwave trough rounding a deep low shifting south
from Hudson Bay is set to cross the Upper Midwest tonight with a
deep second lobe developing over Michigan Sunday that swings south
before tracking over the Interior Northeast Monday night will
provide the likelihood for the first major lake effect and
Appalachian upslope snow event of the season. This reinforcing
trough importantly slows the progress of the surface trough along
the Northeast coast Sunday which prolongs the following flow over
the Great Lakes for lake effect/enhanced snow tonight of Lake
Superior shifting through all the Great Lakes before easing off
Lake Ontario on Tuesday. Strong CAA brings a winter-like airmass to
the region, headlined by 850mb temperatures between negative 10
and 12 degrees C. This cold air (near or below the 10th
climatological percentile) over the warm Great Lakes (temperatures
of +10 to +15C) will result in an impressive convective environment
with model soundings indicating steep lapse rates and deep mixing
heights to near or above 700mb. Given lake temp and 850mb air temp
delta Ts of 20 to 30C, the environment will be rather supportive
for lake effect/enhanced snow production and possible thundersnow.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior tonight through
Monday, Lake Michigan Sunday night through Monday, Lakes Huron and
Erie Sunday night through Monday night, and Lake Ontario Monday
night/Tuesday. Forecast remains uncertain around the Chicago metro
as the north-south Lake Michigan band remains mostly aimed at
northwest IN besides on Monday when the deep upper low passes from
eastern WI into northern IL. This may tug the lake effect band
westward into northeast IL for a period, where snowfall rates
remain impressive and around 2"/hr. Regardless, localized totals
over 1 foot are possible (30-50%) in northwest IN depending on how
long the single Lake Michigan snowband can remain in tact. Days
1-3 WPC probabilities for >8" are over 60-80% in the Huron Mtns of
the U.P. of MI and for portions of the western L.P. shoreline and
all of the Indiana shoreline. Additional 40-60% WPC probabilities
for >8" exist along the shoreline of Lake Erie from northeast OH
into northwest PA and far western NY.

Cold upslope northwesterly flow and a moist fetch from Lake
Michigan will also cause upslope snow showers for the
Central/Southern Appalachians Sunday night through Monday night
with Days 2-3 WPC probabilities for >6" 40-70%.



Snell/Jackson



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FOUS11 KWBC 090907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 AM EST Sun Nov 9 2025

Valid 12Z Sun Nov 09 2025 - 12Z Wed Nov 12 2025

...Michigan to Interior Northeast...
Day 1...

Leading shortwave impulse/vort max over northern IN early this
morning will swing over the Interior Northeast through tonight.
Ongoing deformation zone snow banding north of the associated
surface low tracks over southern MI rest of this morning and the
Buffalo metro this afternoon. Snow rates increase up to 1"/hr
through this swath can be expected as frontogenesis overlaps the
DGZ per the 00Z HREF. WPC probabilities for >4" after 12Z are
20-30% in southeast MI and around 60% over the greater Buffalo
metro.
Warm air advection ahead of this deepening low brings a warm nose
through this evening over northern NY/New England. Light freezing
rain is expected in at least pockets from the Tug Hill through the
Adirondacks and north as well as the White Mtns of NH/ME. WPC
probabilities for >0.1" ice accretion are between 40-70% in
northern NY and closer to 30% for the White Mtns.


...Lake Effect/Enhanced Snow through Tuesday...
Rapidly developing southern lobe of expansive low shifts south over
Michigan today before pivoting east over KY/TN tonight. The
developed low deepens over the northern Mid-Atlantic Monday night
before lifting over New England Tuesday. This will be the first
major lake effect and Appalachian upslope snow event of the
season. This pivoting of the developing low over the Great Lakes
region prolongs the cold air advection flow and thus lake
effect/enhanced snow from Lake Superior through Monday with single
banding likely off Lake Michigan tonight/Monday with
Huron/Erie/Ontario LES late tonight through Tuesday. Favorable QPF
spreads through all the Great Lakes before easing off Lake Ontario
on Tuesday.
The cold airmass, headlined by 850mb temperatures between negative
10 and 12 degrees C over the warm Great Lakes (temperatures of +10
to +15C) will result in an impressive convective environment with
model soundings indicating steep lapse rates and deep mixing
heights to near or above 700mb. Given lake temp and 850mb air temp
delta Ts of 20 to 30C, the environment will be rather supportive
for lake effect/enhanced snow production and possible thundersnow.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior through Monday, Lake
Michigan tonight through Monday, Lakes Huron and Erie late tonight
through Monday night, and Lake Ontario Monday night/Tuesday.
Decent confidence in heavy banding spreading west into the Chicago
metro this evening before drifting back east through Monday
morning. Localized totals over 1 foot are possible (30-60%) in
northwest IN depending on how long the single Lake Michigan
snowband can remain in tact. In addition, Cold upslope
northwesterly flow and a moist fetch from Lake Michigan will also
cause upslope snow showers for the Central/Southern Appalachians
tonight through Monday night with Days 2-3 WPC probabilities for

6" 40-70%. Days 1-2 snow WPC probabilities for >8" are 60-80% in

the Huron Mtns of the U.P. of MI, northwestern Indiana, the central Appalachians/Alleghenies, and southern Appalachian crest. A
forecast of heavy snow is on tap for Monday over the western shore
of MI. Additional 10% Day 2 WPC probabilities for >8" exist along
the shoreline of Lake Erie from northeast OH into northwest PA and
far western NY.



Jackson


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FOUS11 KWBC 092037
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 PM EST Sun Nov 9 2025

Valid 00Z Mon Nov 10 2025 - 00Z Thu Nov 13 2025

...Great Lakes to Interior Northeast and Appalachians...
Days 1-2...

Leading shortwave impulse/vort max lifts northward over Lake
Ontario tonight as an area of low pressure reloads on Monday over
New England as the deep upper low swings across the Ohio Valley.
This setup will provide warm air advection mixed ptype into
northern New England, the northern Adirondacks, and St.Lawrence
river valley through tonight before cold air advection returns to
the region Monday into Tuesday. Light freezing rain is expected in
at least pockets from the Tug Hill through the Adirondacks and
north as well as the White Mtns of NH/ME. WPC probabilities for

0.1" ice accretion are between 30-50%% in northern NY and closer

to 30% for the White Mtns.

...Lake Effect/Enhanced Snow through Tuesday...
Deepening upper-low drops southward from the Great Lakes tonight to
the southern/central Appalachians Monday night, with heights
dropping into record levels for early-mid November. This will lead
to the first major lake effect and Appalachian upslope snow event
of the season as bitter cold Canadian air rushes over the warm
Great Lakes. The pivoting and depth of the developing strong upper
low over the Great Lakes region will prolong the cold air advection
flow and thus lake effect/enhanced snow from Lake Superior through
Monday with single banding likely off Lake Michigan tonight/Monday
with Huron/Erie/Ontario LES late tonight through Tuesday.
Favorable QPF spreads through all the Great Lakes before easing off
Lake Ontario on Tuesday.

The cold airmass, headlined by 850mb temperatures between negative
10 and 12 degrees C over the warm Great Lakes (temperatures of +10
to +15C) will result in an impressive convective environment with
model soundings indicating steep lapse rates and deep mixing
heights to near or above 700mb. Given lake temp and 850mb air temp
delta Ts of 20 to 30C, the environment will be rather supportive
for lake effect/enhanced snow production and likely periods of
thundersnow.

North-northwest to northerly surface winds along with increasingly unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior through Monday, Lake
Michigan tonight through Monday, Lakes Huron and Erie late tonight
through Monday night, and Lake Ontario Monday night/Tuesday.
Decent confidence in heavy banding spreading west into the Chicago
metro this evening as CAMs develop a mesolow over southern Lake
Michigan and help enhance the intense snow rates around 2-3"/hr
along the western shores before drifting back east through Monday
morning. Localized totals over 1 foot are possible (10-20%) in
northwest IN depending on how long the single Lake Michigan
snowband can remain in tact. Here, major impacts are possible due
to very intense snowfall rates and extend into the highly
populated region of northwest IL tonight. In addition, cold
upslope northwesterly flow and a moist fetch from Lake Michigan
will also cause upslope snow showers for the Central/Southern
Appalachians tonight through Monday night with Days 1-2 WPC
probabilities for >6" 40-70%. Days 1-2 snow WPC probabilities for

8" are 30-60% in northeast IL, northwest IN, the central Appalachians/Alleghenies, and southern Appalachian crest.

Additional 50-80% Day 2 WPC probabilities for >8" exist along the
shoreline of Lake Erie from northwest PA into far western NY and
along the southern shoreline of Lake Ontario between Wayne and
Oswego counties. As always the case with lake effect snow, amounts
and impacts could drastically differ over the span of tens of miles
depending on where snowbands situate.



Snell/Jackson





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FOUS11 KWBC 100850
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 AM EST Mon Nov 10 2025

Valid 12Z Mon Nov 10 2025 - 12Z Thu Nov 13 2025

...Great Lakes through Interior Northeast and Appalachians...
Days 1-2...

Deepening upper-low over northern Indiana early this morning swings
southeast over the Ohio Valley today before crossing the Mid-
Atlantic tonight before lifting over New England Tuesday. Strong
and cold northerly flow in the wake of the low persists over Lakes
Superior and Michigan today with northwesterly flow over the
eastern Great Lakes. The cold airmass will have 850mb temps of -10
to -12Z (near the DGZ) which compared to lake temps around +10C will
make for efficient LES banding and a decent, but short lived lake
effect event.

Furthermore, northwesterly flow into the central Appalachians will
make for a decent upslope snow event in West Virginia. Day 1 snow
probs for >6" after 12Z are over 50% in the western shore of MI
from Manistee to Muskegon and south from Holland into north-central
Indiana. Of note, recent HRRRs have maintained the heavy snow
banding in Chicago into the mid-morning hours (longer than
previously forecast). These higher snow probs are also over
northwest PA and the Chautauqua Ridge area of far western New York
and along the southern shore of Lake Ontario as well as the
Allegheny Highlands of WV. As flow becomes more westerly tonight,
the focus over Lake Ontario shifts farther east and includes the
southern Tug Hill to Syracuse where Day 1.5 probs for >6" are
around 40%.

Warm air advection on westerly flow over spreads the eastern Great
Lakes Tuesday night with some higher elevation LES continuing into
Wednesday.


The probability of significant icing is less than 10 percent.


Jackson



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FOUS11 KWBC 101953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 PM EST Mon Nov 10 2025

Valid 00Z Tue Nov 11 2025 - 00Z Fri Nov 14 2025

...Lake effect snow continues across the Great Lakes, Northeast,
and Appalachians through Tuesday, while the next Atmospheric River
event is expected to bring heavy snow for the Sierra Nevada by
Thursday night...


...Great Lakes through Interior Northeast and Appalachians...
Day 1...

Anomalously deep upper trough over the Eastern U.S. and surface low
racing north from the Gulf of Maine into eastern Canada will remain
the driving force behind a cold and windy weather pattern though
the Day 1 period. This will keep the lake effect snow machine
turning as well as upslope snowfall into the Appalachians.
Additionally, a blossoming area of precipitation near the left-
exit region of a 180kt 250mb jet streak is forecast to briefly
impact parts of northern New England.

Starting with the lake effect and upslope snow into the
Appalachians, 850mb flow remains northwesterly to start the Day 1
period but will shift more westerly during the day on Tuesday as
the upper low lifts out of the region and a WAA regime takes hold
through the remainder of the forecast period. This will allow for
Lake Superior and Lake Michigan snowbands to diminish by Tuesday
morning, with better fetch remaining off Lake Erie/Ontario/Huron
through Tuesday night before low-mid level temperatures begin to
warm back to around -5C. Upslope flow into the central/southern
Appalachians also continues early on Day 1 as the southern lobe of
the upper low crosses into western NC to start the period. This may
allow for even some flurries/snow showers to reach eastern NC on
Tuesday morning. WPC probabilities for >4" on Day 1 are 30-50%
along the TN/NC border in the southern Apps and in central WV
Allegheny Mts. For the Lower Great Lakes, WPC probabilities for

8" are 50-80% downwind of Lake Erie from northwest PA to far

western NY as well as downwind of Lake Ontario and the Tug Hill.
Northern VT/NH also have moderate (40-70%) probabilities for >4" of
snow and coincide with 12z HREF highlighting the region for 1"/hr
snowfall rates between 00-03Z tonight.


...Sierra Nevada...
Day 3...

The next Atmospheric River event to impact the West Coast this fall
is forecast to begin impacting the Sierra Nevada with heavy snow by
the end of Day 3 (00Z Friday). Some timing uncertainty remains, as
depicted by the WPC ensemble clusters, with the GEFS suite
primarily faster in moving precipitation onshore. Regardless, this
plume of moisture is poised to be potent with 80% probabilities of

500 km/m/s IVT from the 00z EPS, but progressive and limit extreme

snowfall amounts. Snow levels will start out very high (above
8,000ft) and drop significantly to as low as 5,000ft Thursday night
per the 10th percentile NBM. WPC probabilities for >12" (warning
criteria for the central Sierra) through 00Z Friday are generally
60-80% and above 6,000ft. Additional snowfall is likely after 00Z
Friday.


The probability of significant icing is less than 10 percent.


Snell



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FOUS11 KWBC 110851
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 AM EST Tue Nov 11 2025

Valid 12Z Tue Nov 11 2025 - 12Z Fri Nov 14 2025

...Lake effect snow continues in the Northeast into tonight, while
an Atmospheric River brings heavy snow for the Sierra Nevada
Thursday into Friday...


...Interior Northeast...
Day 1...

Anomalously deep upper low over Upstate New York will lift
northeast over New England today. The Great Lake effect snow
machine shifts focus to the eastern Great Lakes in the wake of the
low as northwesterly flow backs southwesterly tonight. Ongoing LES
bands enriched by Lake Huron that are further enhanced by Lake Erie
will continue to shift into north-central PA and western NY
(especially on the Chautauqua Ridge) with banding southeast of Lake
Ontario between Syracuse and the Tug Hill. These areas have 40-80%
probs for >6" from 06Z today to 06Z Wednesday. The southwesterly
flow tonight allows lake enhanced snow into the Buffalo metro and
the Tug Hill where Day 1.5 snow probs for >6" are around 40% and
80% at the top of Tug Hill. Warm air advection on the southwesterly
flow aids lift, but the thermal profile becomes less supportive of
higher snow ratios. Continued westerly flow Wednesday should allow
higher elevation snows, but at reduced rates.


...Sierra Nevada...
Day 3...

An Atmospheric River impacts California Thursday through Thursday
night ahead of a full-latitude trough that likely spins into a low
off the SoCal coast into this weekend. High moisture plume with PW
of 1.25" to 1.5" brings high snow levels around 9000ft for snow
onset on the Sierra Nevada early Thursday. However, height falls
through the day Thursday allow snow levels to fall to around 6000ft
by Thursday evening and 5000ft early Friday as rates fall off with
the plume pushing to the Baja. Heavy snow can be expected down the
length of the Sierra Nevada with Day 3 snow probabilities for >12"
50-80 percent above about 7000ft and categorical above 9000ft.


The probability of significant icing is less than 10 percent.


Jackson


$$

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FOUS11 KWBC 111948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Tue Nov 11 2025

Valid 00Z Wed Nov 12 2025 - 00Z Sat Nov 15 2025

...Great Lakes and Northeast...
Days 1-3...

Persistent cyclonic flow across the northeast will result in
periods of light to moderate snowfall through Thursday, with
locally heavier lake effect snow also possible. Within this regime,
several shortwave impulses and accompanying vorticity maxima will
rotate southeast, providing renewed impetus for ascent and
resulting snowfall. The first of these will be exiting Downeast
Maine tonight, with rapid drying of the column in its wake leading
to a quick wane of snowfall across Northern New England. However,
this dry period will be somewhat short lived as yet another
shortwave quickly dives through the mid-level NW flow, emerging
from Ontario and shifting into the Mid-Atlantic states by the end
of D1 and into early D2 /00Z Thursday/. This will provide renewed
ascent for snow across much of the area from the U.P. of Michigan
through Northern New England.

During D1, the heaviest snow is likely downwind of Lakes Erie and
Ontario in response to increasing lake effect snow (LES). The setup
is not idea for LES despite warm lake temperatures as winds
gradually veer and mid-level temps modify, reducing the deltaT from
the lake surface to 850mb. Still, a focused band off Lake Erie
early D1, gradually transitioning as flow veers more to the NW by
the evening, will be followed by a focused band off Lake Ontario
later D1 and into early D2. A deepening DGZ is likely into which
theta-e lapse rates collapse suggesting at least a potential for
convective snow rates, but primary ascent below the DGZ and
warming temps aloft my limit the snowfall potential. Still, WPC
probabilities D1 are moderate to high (50-70%) for more than 6
inches of snow across the Tug Hill Plateau, with 2-4" expected

90% chance) near Buffalo, NY and into the far western

Adirondacks.

Then during D2 the elongated vorticity lobe streaks across with
transient height falls and PVA before SW flow later D2 results in
WAA and a reduction in LES, especially west of Lakes Erie and
Ontario. While flow is not ideal along any specific lake D2, an
upstream connection from Huron and the Georgian Bay will help
increase moisture SE of Lake Ontario, leading to a narrow corridor
of heavy snow from the Finger Lakes towards the Catskills. Again,
thermally the column is modest for LES and it is possible the
heavier snow is actually well removed from the lake itself due to
warm lake temps, and WPC probabilities are moderate (30-50%) for
more than 4 inches in parts of the Adirondacks and Greens, as well
as the higher terrain of the Presidential Range. Although snow
accumulations elsewhere across parts of PA, NY, and Northern New
England should be light, briefly heavy rates from convective snow
showers are possible across the region.

By D3, continued NW flow will support some additional modest LES
downstream of Lake Ontario, with upslope flow into VT, NH, and ME
leading to modest snowfall accumulations in the higher terrain of
those states as well.


...California and Nevada...
Days 2-3...

An impressive atmospheric river (AR) will spread onshore CA
beginning Wednesday night and persisting through Thursday. This AR
will be characterized by impressive IVT reflected by high
probabilities (>80% chance) of exceeding 750 kg/m/s, reflecting a
strong AR moving into CA, and in fact the +1 sigma within the
ensembles are above 1000 kg/m/s, which is above the climatological
record for mid-November according to NAEFS ensemble tables. This
will result in significant and heavy precipitation spreading into
CA Thursday and Friday.

The driver of this robust AR is a strong closed low moving across
the northern Pacific which will approach the CA/OR coast late
Thursday and then slowly open before moving onshore northern CA
Friday. This will result in strong ascent through the overlap of
height falls and narrow but impressive LFQ diffluence as a jet
streak pivots onshore as well. Despite the slow motion of this
upper low, the best moisture within the AR will be somewhat
transient, so the duration of heavy precipitation in any one
location across CA will be somewhat limited (around 24 hours), and
with pronounced WAA within the core of the AR, most of this
precipitation should fall as rain. However, the exception is likely
to be across the Sierra, initially above 8000 feet, then falling
to around 5000-5500 ft behind a cold front which will push eastward
into the Great Basin by Friday morning.

This lowering of snow levels will allow for heavy accumulations
across the Sierra, leading to significant impacts at the area
passes. WPC probabilities on D2 are high (>70%) for 6+ inches of
snow in the Sierra, but generally above 7000-8000 ft. As snow
levels lower D3, WPC probabilities indicate an additional high
chance (>90% in the higher terrain) of 6+ inches, leading to
event-total snowfall in the Sierra of 2-3 feet. This will produce
dangerous travel at many of the Sierra passes, with a heavy and wet
snow contributing to an increased chance for at least moderate
impacts from the WSSI-P due to snow load and snow amount.

Additional heavy snow is expected on D2 near Mt. Shasta, and on D3
extending into the Great Basin and some of the higher terrain of
Nevada.


...Pacific and Interior Northwest...
Day 3...

A sharp vorticity maxima will shed from the closed low approaching
CA (referenced above) and move onshore Washington State Friday.
This feature will be transient and of modest amplitude, but will
encounter elevated PWs as the S/SW AR downstream of the primary low
will spread higher moisture northward. This vorticity maxima may
lead to subtle surface low development as shown by some of the
ensembles, which would additionally enhance ascent, at least
briefly, followed by more confluent zonal mid-level flow in its
wake. While there are considerable differences among the various
models by Friday with respect to available moisture and timing of
these features, it appears likely that some heavy snow will occur
across the Cascades and potentially spread into portions of the
Northern Rockies, especially above 4000 ft in the Cascades and 5000
ft farther east. This will result in snowfall accumulations that
have a 30-50% chance of exceeding 6 inches, primarily in the higher
elevations of the Washington Cascades.


The probability of significant icing is less than 10 percent.


Weiss

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FOUS11 KWBC 120842
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
342 AM EST Wed Nov 12 2025

Valid 12Z Wed Nov 12 2025 - 12Z Sat Nov 15 2025


...California...
Days 2-3...

A potent, but transient atmospheric river (AR) shifts into far
northern California late Wednesday night and works its way down the
length of the state through Friday. Of particular note with AR is
confidence on the upper trough axis stalling along the northern CA
coast Thursday night instead of shifting inland as previous model
consensus solutions had forecast. Instead, height falls are not as
great over the Sierra Nevada and snow levels are now forecast to
remain above 8000ft for most of the heavy precip and only drop to
around 6000ft Friday morning over the northern Sierra Nevada which
is once rates have dropped off. Heavy snow will still occur over
the High Sierra from Thursday afternoon through Friday morning,
but confidence has risen that the 6" snow contour should generally
stay above 8000ft on the Sierra Nevada which is far less impactful
than prior forecasts with lower snow levels. WPC probabilities for

12" from 18Z Thursday to 18Z Friday are 50-90% above about 8500ft.

The reason for this warmer solution is the trough that digs down
the coast closes off into a low off SoCal late Friday where it
lingers through Saturday before shifting inland. Warm air advection
east of this low over SoCal keeps snow levels 9000ft or above
through Saturday keeping accumulating snow to pretty much just the
highest peaks of the San Bernardino Mtns.

The higher snow levels also apply to Nevada where the only highest
peaks have any shot at >4" snow through Friday night.


...Pacific Northwest through the Northern Rockies...
Days 2-3...

The northern portion of the full-latitude trough axis off the West
Coast reaching the PacNW coast late Thursday and works its way east
across the northern Rockies through Friday. High snow levels in the
warm air advection ahead of the trough generally drop to around
5000ft Thursday night in the Washington Cascades progressing east
during the day Friday over northern ID/MT ranges. Limited moisture
due to the base of the trough being well down off CA keeps precip
rates low to moderate. Day 2 snow probs for >4"are 40-60% over the
highest Cascades and around North Cascades NP.

Moisture spreading east with the trough axis on Friday brings
moderate snow to central ID north through Glacier NP, as well as
northwest WY where Day 3 snow probs for >4" are 30-70%. Continued
flow over the Cascades with snow levels dipping around 4500ft early
Friday brings moderate snow there with snow probs for >6" 40-80%
over the Washington Cascades.


...Interior Northeast...
Days 1-2...

Troughing continues over the Northeast through Thursday before a
low develops over the Canadian Maritimes. The next shortwave trough
axis is currently over eastern Ontario with southwesterly flow
overspreading Lakes Erie and Ontario to lake enhanced precipitation.
This warm air advection makes for marginal thermal profiles which
requires some elevation increase from lake level for snow
accumulation. The trough axis shifts east over Upstate NY this
afternoon and brings a return to northwesterly flow (and some cold
air advection) over the eastern Great Lakes for tonight. This
should allow some snowfall downstream of Lake Ontario east of the
Finger Lakes into the Catskills. Day 1 snow probabilities for >4"
are 40-70% for the Tug Hill, Adirondacks, Greens, and higher Whites
of NH with a few blips of 20% south of the Mohawk Valley in NY.

This northwesterly flow pattern persists over the Northeast through
Thursday night with some additional cold air advection allowing for
snow levels to drop a bit, particularly under an impulse passage
Thursday evening. Day 2 snow probs for >4" are 20-60% south of the
Mohawk Valley along with the northern Adirondacks, and more of the
Greens and Whites (where probs reach 80%). Only light snow is
forecast on Northeast terrain in the flow wrapping around the
developing low north of Maine on Friday.

The probability of significant icing is less than 10 percent.


Jackson



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FOUS11 KWBC 122011
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 PM EST Wed Nov 12 2025

Valid 00Z Thu Nov 13 2025 - 00Z Sun Nov 16 2025


...California...
Days 1-3...

A strong 750+ kg/m/s atmospheric river (AR) will begin to make
landfall across far northern California late tonight before
gradually working its way down the length of the state through
Saturday. This potent but transient AR will transport copious
amounts of moisture (PW anomalies in excess of 250-300% of
normal), leading to heavy mountain snows across the Sierras the
next few days (particularly Day 2). Recent model trends advertising
the slower inland progression of a cut-off upper low off the coast
of California continue today, leading to higher snow levels above
8-10kft within an extended WAA regime through the period.

The latest WPC 72-hr snow probabilities >12" across the Sierras
(above 8kft) are high (70-95%) while probabilities >24" are
moderate (40-70%).


...Pacific Northwest through the Northern Rockies...
Days 2-3...

North of the cut-off low off the coast of California, a sheared off
shortwave will reach the Pacific Northwest coast late Thursday and
work its way east across the northern Rockies through Friday. High
snow levels above 8-9kft in the warm air advection ahead of the
trough generally drop to around 5kft late Thursday into
Friday. Given the separation between the northern shortwave and the
cut-off low/atmospheric river well to the south, available moisture
will be fairly limited across the Pacific Northwest. This should
keep snowfall rates across the high terrain low to moderate.

The latest Day 2-3 WPC 48-hr snow probabilities >8" across the
Washington Cascades and northern Rockies are moderate (40-80%).


...Interior Northeast...
Days 1-2...

Persistent troughing continues over the Northeast the next few
days as a series of impulses move through the northwesterly flow
aloft. These impulses combined with a renewed cold advection regime
blowing across the warm eastern Great Lakes will result in bands
of lake enhanced precipitation. This will likely lead to some
additional snowfall downstream of Lake Ontario east of the Finger
Lakes into the Catskills. Cold upslope flow will also lead to
persistent snowfall across portions of the northern Adirondacks,
Greens, and higher Whites of New Hampshire. Only light snow is
forecast on Northeast terrain in the flow wrapping around a
developing low north of Maine later Friday into Saturday.

The latest Day 1 WPC 24-hr snow probabilities for >4" are moderate
(30-70%) across portions of the Tug Hill, Adirondacks, and east of
the Finger Lakes into the Catskills. Meanwhile, Day 1-2 48-hr snow probabilities for >12" are moderate (40-80%) across the Greens,
and higher Whites, with 20-40% probabilities for >18".


The probability of significant icing is less than 10 percent.


Miller






$$

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