• HVYSNOW: Blizzard Predict

    From Dumas Walker@21:1/175 to All on Monday, December 19, 2022 16:34:00
    FOUS11 KWBC 192056

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    356 PM EST Mon Dec 19 2022

    Valid 00Z Tue Dec 20 2022 - 00Z Fri Dec 23 2022

    ...Arctic cold front pushes down the Plains with Blizzard
    conditions for portions of the Plains and Midwest...

    ...Pacific Northwest, Northern Rockies, and Northern High Plains...
    Days 1-2...

    An upper trough currently over the Gulf of Alaska will wrap around
    a deep upper low currently centered over the Canadian Rockies
    through Tuesday before shifting southeast down the northern
    Rockies and northern High Plains Tuesday night and Wednesday. A
    plume of Pacific moisture ahead of the Gulf of Alaska wave will
    shift across WA and the northern ID/MT Rockies tonight before
    shifting south to northern OR and southern ID/MT Rockies.

    Snow levels near sea level and moderate to locally heavy precip
    rates along a nearly stationary arctic cold front look to cause
    notable accumulations across Washington tonight including the
    Seattle metro area along with enhanced snowfall in mountains.
    Moderately high Day 1 snow probabilities for over 4 inches are
    across the Puget Sound area with high probabilities for a foot or
    more for the Olympics and WA Cascades with moderate probabilities
    for over 8 inches in the northern ID/MT Rockies including the

    The favorable upper forcing and strong low-to-mid level
    frontogenesis will support heavy mountain snow spreading east from
    the Pacific Northwest into the northern and north-central Rockies
    Tuesday through Wednesday. Day 2 snow probabilities for more than
    8 inches are high again for the Bitterroots as well as the
    Absarokas, Tetons, and Wind River Range in WY with 48hr totals in
    both these mountainous areas having high probabilities for over 18

    In addition, as the upper trough begins its push southeast down
    the northern Rockies Tuesday night the advancing arctic cold front
    looks to be accompanied by lines of heavy snow and likely snow
    squalls that spread over ID/WY Tuesday night/Wednesday and
    possibly northern Colorado late Wednesday. Please see Key messages

    By Tuesday afternoon, favorable upper divergence associated with a
    left-exit region of a strong NWly 250mb jet streak coming in from
    the North Pacific will help spread overrunning precipitation into
    the northern High Plains of Montana. Surface temperatures will be
    extremely cold and well below zero during this timeframe, which
    may actually temper SLRs from exceeding 20 to 1. Day 1.5 snow
    probabilities for 6 inches or more are high for much of
    west-central Montana mountains and valleys with the Big Belt
    Mountains forming much of the eastern boundary.

    ...Northern and Central Plains through the Midwest/Great Lakes...
    Days 2-3...

    The aforementioned upper trough currently over the Gulf of Alaska
    that pushes down the northern Rockies/northern High Plains Tuesday
    night with an arctic cold front pushing south into the central
    Plains Wednesday into early Thursday will have impressive fgen,
    enhanced upper level jet support, and very cold air. This will
    allow for development of widespread moderate snowfall amounts
    Wednesday over the eastern Dakotas that then spreads south through
    Nebraska and east through much of Minnesota and northwest Iowa.
    Day 2 snow probabilities for more than four inches are centered
    near the Buffalo Ridge of southwest MN.

    Lee-side cyclogenesis ahead of the arctic cold front dips south to
    the TX Panhandle late Wednesday before shooting east to the MO/AR
    border by early Thursday then rapidly intensifying as it turns
    northeast up the Midwest through Thursday. This will allow for
    further expansion of the snow areas along with development of
    heavy snow bands. This is seen in the Day 3 snow probabilities
    which for 4 or more inches are moderate or higher from
    west-central KS to central MO and northeast to the western Great
    Lakes. Embedded are moderate probabilities for 8 or more inches
    from southeast Neb, northwest MO through central IA to southeast

    The presence of an existing wave moving along the Gulf Coast today
    through Tuesday will limit the amount of Gulf moisture available
    to the mid to late week system. Gulf moisture begins to stream
    ahead of the system starting on Wednesday which will allow further
    development of heavy snow bands for Thursday. Enhanced lift within
    a deep DGZ for much of the central Plains and into the Upper
    Midwest will support very efficient SLRs to make up for the lack
    of initial moisture, along with surface temperatures around zero
    behind the arctic cold front. High SLRs above 20 to 1 may be
    short-lived for much of the central High Plains, as strong low to
    mid-level winds above 50 kts fracture the falling dendrites.
    However, the gusty winds (and extremely low wind chills) will add
    to the potential for dangerous travel as visibility decreases and
    blowing snow ensues. This system will continue to progress
    eastward and become a large and powerful storm set to impact much
    of the Midwest and Great Lakes with potentially heavy snow through
    late this week and into the Holiday Weekend. Of particular note is
    the slow motion which will allow for long duration of heavy snow
    bands, particularly over the central Great Lakes.

    ...Southern/Central Appalachians...
    Day 3...
    In response to the deepening trough over the central U.S. on
    Wednesday, moisture return along the East Coast will enter the
    southern Mid-Atlantic and ride up along the southern and central
    Appalachians Wednesday night into Thursday morning. A strong
    surface high depicted by all guidance over New England during this
    time frame will support cold air damming into Thursday morning and
    the at least localized freezing rain over mainly the higher
    terrain west from the Blue Ridge Mountains. Day 3 WPC
    probabilities for at least a tenth of an inch of ice accretion are
    moderate across western NC, southwest Virginia, eastern WV, into
    west-central PA. The threat of freezing rain is expected to
    persist into Thursday night until the arctic cold front blows
    through and changes to accumulating snow.

    Key Messages for Blizzard
    --Significant Blizzard Developing this Week
    An area of low pressure will develop Wednesday night and then
    strengthen while lifting northeast into the Great Lakes by Friday
    morning. This will result in blizzard conditions across portions
    of the Central/Northern Plains, Upper Midwest, and Great Lakes.

    --Extremely Dangerous Travel Conditions
    Heavy snowfall rates of 1-2 inches per hour at times, along with
    wind gusts of over 50 mph will result in near zero visibility and
    considerable blowing and drifting of snow. This will lead to
    dangerous, to at times impossible, land and air travel leading up
    to the holiday weekend.

    --Potential for Impacts to Infrastructure
    The combination of heavy snow and strong wind gusts could lead to
    significant infrastructure impacts as well, including scattered
    tree damage and power outages.

    --Dangerous Cold along with the Blizzard
    Dangerous wind chills will accompany the blizzard, creating a
    significant hazard for anyone that becomes stranded. Prepare now
    for extreme cold and ensure outdoor animals and livestock have
    sufficient shelter.

    --Flood Threat for the Interior Northeast
    Farther east, heavy rain falling onto a melting snowpack will
    cause flooding concerns across the Northeast.

    Key Messages for Cold Front and Snow Squalls
    --Dangerous Cold for Much of Country
    A combination of frigid temperatures and gusty winds behind an
    Arctic cold front will bring dangerously cold conditions across
    most of the country this week, and to the Eastern U.S. by week..s

    --Rapid Temperature Drops with Front
    Arctic air will arrive quickly behind the cold front, with
    temperatures likely to drop 25 to 35 degrees in just a few hours
    as the front passes a given location.

    --Hazardous Snow Squalls in the West
    Snow squalls may lead to hazardous travel in the Western U.S. from
    Tuesday Night into Wednesday. Snow rates over 1 inch per hour and
    gusty winds may lead to sudden whiteout conditions.

    --Flash Freeze Possible Farther East
    From the Mid-South to the East Coast, rain before the Arctic front
    could freeze in the rapidly falling temperatures and lead to icy
    roads and hazardous travel.


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