• Storm Prediction Center 10 07

    From LU9DCE@21:5/101 to ALERT on Wed Jul 10 04:10:14 2019
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    SPC 1200Z Day 1 Outlook
    Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258
    AM CDT Wed Jul 10 2019
    Valid 101200Z - 111200Z
    ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
    GREAT LAKES AND SOUTHERN PLAINS...
    ...SUMMARY... Severe thunderstorms are possible Wednesday into
    Wednesday night across portions of the upper Great Lakes and
    southern Plains.
    ...Synopsis... Shortwave trough currently moving through the
    central Plains will continue eastward through the Upper Midwest
    and Upper Great Lakes on Wednesday. Surface low attendant to this
    upper system will move eastward across western Ontario. A second,
    weaker low may develop over the Upper Great Lakes Wednesday evening
    as height falls promote secondary cyclogenesis. An associated cold
    front will sweep southeastward/southward across the central/southern
    Plains, Upper Midwest and middle MS Valley. By 00Z Thursday, this
    cold front is expected to extend from eastern Upper MI southeastward
    through central IL, central MO, northern OK and into the northern
    TX Panhandle.
    Upper ridging will remain in place across the southern third of the
    CONUS with the western portion of this ridge (centered near the Four
    Corners) expected to build throughout the period. A shortwave trough
    will move through the northwestern periphery of this ridge across
    the Pacific Northwest and northern Rockies. Additionally, area of
    low pressure currently over the central FL Panhandle is expected
    to continue drifting southward, moving into the western Gulf of
    Mexico early Wednesday. Some organization/strengthening of this low
    is expected as it moves gradually westward across the northern Gulf.
    ...Upper Great Lakes to Mid-MS Valley... Thunderstorms will
    likely develop along the cold front as it pushes through the region
    Wednesday afternoon. The strongest forcing for ascent is anticipated
    across the Upper Great Lakes, where frontal convergence and height
    falls will be maximized. Strongest flow aloft and vertical shear
    will also exist across this area. The resulting combination of
    forcing for ascent, favorable vertical shear, and ample low-level
    moisture will support organized thunderstorm development. Primary
    threat will be strong wind gusts with some hail also possible. A
    tornado or two is possible, particularly if areas of enhanced
    southerly surface wind develop.
    Farther south, less convergence along the front, displacement south
    of the strong large-scale forcing for ascent, and warmer temperatures
    aloft, will temper thunderstorm coverage. Even so, ample low-level
    moisture will foster strong buoyancy and any storms that do develop
    could pose a risk for isolated damaging wind gusts and hail.
    ...Southern Plains into the Ozark Plateau... Strong cold pool
    generated by early morning storms across the central Plains is
    expected to surge quickly southward/southeastward, augmenting the
    cold front, with this composite boundary reaching the northern TX
    Panhandle, northern OK, and southeast MO by the afternoon. Very
    moist and unstable air mass will be in place ahead of this outflow
    and guidance is in good agreement that convective initiation occurs
    along much of this boundary around 18Z. Vertical shear is weak,
    but steep low-level lapse rates and relatively high LCLs amidst a
    very moist environment support the potential for strong downbursts.
    ...Central Gulf Coast... Very moist profiles (with PW values
    over 2.25") will limit instability, with predominantly warm-rain
    processes anticipated. Even so, a few stronger updrafts may result
    in enough water-loading to product damaging wind gusts. Additionally,
    as this area of low pressure organizes and deepens, low- to mid-level
    flow is expected to gradually strengthen. The amount of deepening
    and resulting low- to mid-level wind speeds is uncertain, but the
    potential exists for enough vertical shear to develop to support
    an isolated tornado threat.
    ..Mosier/Wendt.. 07/10/2019
    SPC 0600Z Day 2 Outlook
    Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1148
    PM CDT Tue Jul 09 2019
    Valid 111200Z - 121200Z
    ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THURSDAY AFTERNOON
    AND EVENING ACROSS THE MUCH OF THE ALLEGHENY PLATEAU/UPPER OHIO
    VALLEY AND ADIRONDACKS REGION...
    ...SUMMARY... Strong thunderstorms posing a risk for potentially
    damaging wind gusts are expected to develop across parts of the
    upper Ohio Valley and lower Great Lakes region Thursday afternoon,
    then gradually spread across and east of the Appalachians through
    Thursday evening.
    ...Synopsis... A broad area of mid-level subtropical ridging,
    centered over the southern Rockies, appears likely to remain
    prominent across much of the western and central U.S. through
    this period. While broad troughing lingers within the mid-latitude
    westerlies across the northeastern Pacific, this flow will transition
    to broadly anticyclonic inland of the Pacific Northwest coast
    through the Canadian/U.S. border area and Upper Midwest. A short
    wave impulse emanating from the troughing, may accelerate eastward
    within this regime. However, it still appears most probable that
    associated forcing for large-scale ascent will remain north of the international border through 12Z Friday.
    Downstream, an initially more significant short wave trough is
    expected to progress east and southeast of the Great Lakes/Ohio
    Valley region Thursday through Thursday night. As it does, models
    continue to indicate that there may be some weakening, with the
    strongest embedded smaller-scale impulse, initially northeast of
    Lake Huron/Georgian Bay, migrating into and through southern Quebec.
    But, a fairly well defined cold front is still forecast to advance
    east of the lower Great Lakes, and across/south of the Ohio River
    by the end of the period.
    ...Lower Great Lakes/Ohio Valley into Mid Atlantic... The
    pre-frontal environment likely will be characterized by seasonably
    high moisture content (including surface dew points in the upper
    60s to lower 70s F), with a corridor of stronger surface heating
    contributing to at least moderate mixed-layer CAPE on the order of
    1000-2000+ J/kg across the Ohio Valley/Cumberland Plateau region
    through much of the Allegheny Plateau and Adirondacks by Thursday
    afternoon. Given this destabilization, forcing for ascent ahead
    of the upper troughing probably will be sufficient to support the
    initiation of considerable thunderstorm development.
    As activity gradually grows upscale through the afternoon,
    consolidation and strengthening of surface cold pools is expected to
    lead to an increasing risk for potentially damaging wind gusts. It
    appears that this risk, and convective organization, will be enhanced
    by modest deep layer shear beneath 30+ kt southwesterly/westerly
    flow in the 700-500 mb layer. Clusters of storms developing across
    the upper Ohio Valley may spread across and east of the Allegheny
    Mountains with a continuing risk for damaging wind gusts before
    diminishing late Thursday evening.
    ...Central and eastern Gulf Coast... There remains at least a modest
    signal in latest model output that intensifying southerly low-level
    wind fields, on the eastern flank of a strengthening tropical
    cyclone, may impact the region by late Thursday/Thursday night.
    There may be coinciding enhancement of low-level convergence, and
    enlarging low-level hodographs, near immediate coastal areas to
    support convection capable of producing either relatively brief/weak
    tornadoes, or locally strong surface gusts.
    ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind:
    15% - Slight Hail: 5% - Marginal
    ..Kerr.. 07/10/2019
    SPC Day 1 Fire Weather Outlook
    Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
    1259 AM CDT Wed Jul 10 2019
    Valid 101200Z - 111200Z
    ...NO CRITICAL AREAS...
    ...Synopsis... An upper-level ridge will continue to build in the
    Four Corners region today. Widespread weak winds across the Great
    Basin and Desert Southwest will keep fire weather concerns to a
    minimum. Locally elevated conditions may occur in southern/central
    Nevada as a thermal surface low enhances southerly flow during
    the afternoon. A few isolated thunderstorms are also possible
    along/north of the Mogollon Rim from east-central Arizona into
    north-central Arizona. Slow storm motions and recent rainfall,
    particularly in eastern portions of the Rim, will limit overall
    spatial extent of lightning ignition risk. Furthermore, 100/1000-hour
    fuel moisture remains near normal according to latest SWCC guidance.
    ..Wendt.. 07/10/2019
    ...Please see www.spc.noaa.gov/fire for graphic product...
    SPC Day 2 Fire Weather Outlook
    Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK
    0144 AM CDT Wed Jul 10 2019
    Valid 111200Z - 121200Z
    ...Synopsis... Upper-level ridging will continue to be centered
    over the Four Corners region on D2/Thursday. Monsoonal moisture will
    lift northward into Arizona and Utah. At least isolated coverage of thunderstorms is expected across much of the Mogollon Rim into the
    central mountains of Utah with the aid of subtle mid-level shortwave
    troughs. A dry sub-cloud layer is expected to develop prior to
    convection in the afternoon with RH falling as low as 10-15%. A more
    mixed wet/dry mode is expected across the Mogollon Rim where PWAT
    will be greater as well as storm motions being slower. A higher
    concentration of drier storms will occur in central Utah on the
    edge of the mid-level moisture where storm motions are forecast
    to be faster. Continued drying of fuels at higher elevations,
    particularly heavier fuels, will support at least a marginal risk
    of lightning ignitions in the highlighted area.
    ..Wendt.. 07/10/2019
    ...Please see www.spc.noaa.gov/fire for graphic product...

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