• North Plains Winter Storm

    From Dumas Walker@21:1/175 to All on Thursday, March 21, 2024 08:18:00
    FOUS11 KWBC 210819
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    419 AM EDT Thu Mar 21 2024

    Valid 12Z Thu Mar 21 2024 - 12Z Sun Mar 24 2024

    ...Pacific Mountain Ranges... Days 2-3...

    A large, barreling upper low off the West Coast on Friday will
    begin directing a healthy fetch of 850-700mb moisture at the
    Pacific Northwest and northern California. NAEFS is indicating an
    IVT of 300-400 kg/m/s (>90th climatological percentile) will
    steadily work its way into California on Friday. This IVT will be
    the primary driver in producing heavy snowfall in the
    Salmon/Siskiyou Mountains of northern California, as well as along
    the spine of the Sierra Nevada. These mountain ranges also reside
    beneath the diffluent left-exit region of 180kt 250mb jet streak
    located off the Southern California coast Friday night. NAEFS is
    showing 200mb winds Friday afternoon and into Saturday that are
    above the observed 200mb wind speeds within the CFSR climatology
    database for this time of year. This shows that along with the
    usual strong upslope ascent, that impressive synoptically-forced
    ascent will be present as well.

    Snow levels will initially start out between 4,000-5,000ft Friday
    night but drop to as low as 3,000ft by Saturday as the upper
    trough moves into the Northwest. However, snow totals that likely
    surpass 12" will be at elevations >5,000ft Saturday and through
    Sunday morning. Farther north, while the moisture transport is not
    as prevalent, the Pacific Northwest lies directly ahead of the
    approaching upper low, which will still support prolonged
    synoptically-forced ascent aloft and lowering snow levels. Snow
    levels will be a near carbon-copy of the scenario farther south in
    the California Ranges, but the Cascades Range and Olympics
    5,000ft will have the best odds of seeing cumulative snowfall
    totals top 12 inches for this event. As the upper low moves ashore
    and over the Northwest on Saturday, the axis of Pacific moisture
    will be directed farther inland as well, leading to periods of snow
    for elevations >6,000ft in the Great Basin, the Blue Mountains of
    eastern Oregon, the Boise/Sawtooth of Idaho, the Tetons and
    Absaroka, and event as far inland as the Wasatch and Colorado
    Rockies by Saturday night. WPC PWPF has identified the Sierra
    Nevada as the only mountain range sporting high chances (>70%) for
    snowfall totals >12". Once the snowfall threshold dips to 6",
    however, just about every aforementioned mountain range above
    sports moderate-to-high chances (50-80%) for >6" of snowfall l;ate
    Friday night and through Saturday night as well.

    ...Northern Rockies & Northern High Plains... Days 2-3...

    Even in wake of the storm system that tracked into the Upper
    Midwest Thursday night, the large dome of high pressure over the
    Canadian Prairies and lower pressure in the West continues to
    support a prolonged low-level easterly flow regime into the western
    Montana Rockies, as well as far south as the Absaroka and Big
    Horns of northern Wyoming. Another 700mb FGEN band will strengthen
    throughout the day Friday and into Friday night as 700mb WAA
    increase over the northern High Plains. In addition, much of
    Montana lies beneath the divergent right-entrance region of a 100kt
    250mb jet streak. This is a recipe for periods of snow on Friday,
    however snowfall rates will not come down heavily enough during
    the day on friday to do much more than Minor Impacts. Snow will be
    able to accumulate better Friday night once the sun sets.

    By Saturday morning, the approaching upper low positioned over the
    Pacific Northwest will spawn a new surface low somewhere over
    eastern Idaho Saturday morning that then tracks into northern
    Wyoming by Saturday evening. This new surface low grows to become
    rather anomalous, eventually dropping below the 1st climatological
    percentile according to NAEFS over central Wyoming Saturday
    evening. To the north of this surface low, easterly 850mb winds
    will increase in strength from central Montana to the Dakotas to
    the point where 850mb zonal wind anomalies also dip below the 1st climatological percentile. These 850mb winds will also direct a
    surge of 850mb moisture flux that originates from a LLJ that
    originates as far south as the Lower Rio Grande Valley. With a
    strengthening low pressure system emerging into the northern High
    Plains Saturday night and cold Canadian High Pressure anchored to
    the north, all the ingredients are coming together for a potential
    significant winter storm from the northern Rockies to the Northern
    Plains this weekend. This far out, however, there remains
    uncertainty in storm track, duration, precipitation type, and of
    course, snowfall totals.

    Between 12Z Friday - 12Z Saturday, WPC PWPF shows the Lewis Range
    as having low chances (10-30%) for >6" of snow with elevations
    6,000ft most favored. By 12Z Saturday - 12Z Sunday, the low-to-
    moderate chance swath (30-50%) for >6" of snowfall grows
    substantially to include most of the northern Rockies in elevations
    6,000ft, through central and eastern Montana, and into western
    North Dakota. Of course, the storm system will continue to produce
    heavy snow and blustery winds into Sunday, so those potentially in
    the path of this impending winter storm will want to check in with
    their local WFO and our WPC medium range suite of products of the
    latest regarding this winter storm for Sunday and into next Monday.

    Mullinax


    ***Key Messages for Northern Plains Winter Storm March 23 - March 26***

    -- Winter storm becoming likely:
    Confidence continues to increase that a large storm system will
    produce a swath of heavy snow, freezing rain, and sleet across
    portions of the Northern Plains and Upper Midwest into early next
    week.

    -- Widespread heavy snow:
    Heavy snow is expected to overspread eastern Montana late
    Saturday,
    then expand into the Northern Plains and Upper Midwest by Sunday
    night, producing significant accumulations. Snow should exit the
    area during Tuesday.

    -- Significant impacts due to snow, ice, and wind:
    A combination of heavy snow and gusty winds, as well as freezing
    rain south of the heavy snow, will likely produce areas of
    hazardous travel and impacts to infrastructure.

    -- Forecast changes anticipated:
    Uncertainty remains with the timing and location of the storm
    track, which will affect where the most significant impacts will
    occur. Keep up to date with the latest forecast as this storm
    evolves.

    $$
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  • From Dumas Walker@21:1/175 to All on Friday, March 22, 2024 09:27:00
    FOUS11 KWBC 220807
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    407 AM EDT Fri Mar 22 2024

    Valid 12Z Fri Mar 22 2024 - 12Z Mon Mar 25 2024

    ...Northern Rockies & High Plains, Central Rockies, Upper Midwest...
    Days 2-3...

    **Significant late season winter storm becoming increasingly likely
    from the Northern Rockies and Northern High Plains to as far east
    as the Upper Midwest this weekend

    In wake of the storm system that tracked through the Upper Midwest
    Thursday night, the large dome of high pressure over the Canadian
    Prairies working in tandem with lower pressure in the West supports
    a prolonged low-level easterly easterly flow regime into the
    western Montana Rockies as well as central Montana and as far south
    as the Absaroka and Big Horns. Another 700mb FGEN band will
    strengthen throughout the day today and into Friday night as 700mb
    WAA increases over the northern High Plains. In addition, much of
    Montana lies beneath the divergent right-entrance region of a 100kt
    250mb jet streak. This is a recipe for periods of snow today,
    however snowfall rates will not come down heavily enough during the
    day to do much more than Minor Impacts. Snow will accumulate more
    effectively Friday night.

    By Saturday morning, the approaching upper low in the Pacific
    Northwest will spawn a new surface low somewhere over eastern Idaho
    Saturday morning that will track into northern Wyoming Saturday
    evening. The surface low will continue its trek southeast into
    eastern Colorado, where NAEFS suggests it will eventually reach
    MSLP values that are <0.5 climatological percentile. Meanwhile, the
    850mb LLJ will accelerate over the Great Plains with winds topping
    the 97.5 climatological percentile over the southern Great Plains
    around 06-12Z Sunday. The LLJ will advect anomalous 850-700mb
    moisture northward and wrap around the northern flank of the
    strengthening surface low, and give rise to a blossoming shield of
    heavy snow early Sunday morning from western Montana and northern
    Wyoming to the Dakotas. Strong 850-700mb WAA and copious amounts of
    Gulf of Mexico moisture will make its way into the Upper Midwest
    where heavy snow will then ensue over southern Minnesota. By 00Z
    Monday, a significant winter storm will be well underway, causing
    strong winds and heavy snow from the Central Rockies on east
    through the Black Hills, the Dakotas, and into the Upper
    Mississippi Valley. NAEFS by 00Z Monday shows MSLP values in parts
    of southwest Kansas and the TX/OK Panhandles that fall outside the
    observed MSLP minimum for this time of year (~980mb), showcasing
    the remarkable strength this storm will reach Sunday evening. By
    early Monday morning, the storm will track northeast towards the
    Missouri River with a pronounced TROWAL over the eastern Dakotas
    and western Minnesota being the focus for the heaviest snowfall.

    There remains some uncertainty in regards to the position and track
    of the storm, but most ensemble members are on board with this
    becoming an impressive late March winter storm. Latest WSSI-P shows moderate-to-high chances (50-80%) for Moderate Impacts from
    eastern Montana and along the ND/SD border to south-central
    Minnesota through early Monday morning. There are similar
    probabilities for Moderate Impacts that stretch as far south as the
    Sand Hills of northern Nebraska. There are even some low-to-
    moderate chances (30-50%) for Major impacts in parts of eastern
    South Dakota, southwest Minnesota, and throughout the Twin Cities
    metro area. The primary drivers in the WSSI-P algorithm are Snow
    Amount and Blowing Snow, the latter of which, shows >60% chances
    for Minor Impacts as far south as the Palmer Divide and into
    central Nebraska as a powerful cold front passes through these
    areas on Sunday. There are more details on the event in the Key
    Messages below, but residents in these areas are encouraged to
    closely monitor the latest forecasts this weekend as this storm
    will likely continue to cause hazardous impacts for parts of the
    Northern Plains and Upper Midwest into the start of next week.


    Mullinax


    ***Key Messages for Northern Plains Winter Storm***

    --Significant winter storm likely

    Confidence continues to increase in a large storm system that will
    produce an area of heavy snow over the Northern Plains and into the
    Upper Midwest, along with some areas of mixed precipitation this
    weekend into early next week.

    --Widespread heavy snow expected

    Heavy snow is forecast to overspread eastern Montana late Saturday,
    then expand into the Northern Plains and Upper Midwest by Sunday
    afternoon. There is a high chance (>70%) of at least eight inches
    of snow from the North Dakota/South Dakota border eastward into
    Minnesota and northern Wisconsin.

    --Hazardous impacts due to snow, snow load, and wind

    A combination of heavy snow and gusty winds will likely produce
    areas of blowing and drifting snow, as well as possible blizzard
    conditions Sunday into Monday. Hazardous travel, along with some
    disruptions and closures are expected late Saturday into Monday.
    The combination of strong winds and heavy, wet snow on trees and
    power lines may result in tree damage and power outages.

    --Additional forecast changes anticipated

    Uncertainty remains with precipitation type for southern-most areas
    and a possible sharp northern snowfall gradient in northern-most
    areas. Closely monitor the latest forecasts as the storm evolved
    over the next 24-48 hours.

    $$
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