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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