• Winter Storm North Plains

    From Dumas Walker@21:1/175 to All on Wednesday, March 20, 2024 07:55:00
    FOUS11 KWBC 200857

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    457 AM EDT Wed Mar 20 2024

    Valid 12Z Wed Mar 20 2024 - 12Z Sat Mar 23 2024

    ...New England...
    Days 1-2...

    A potent shortwave trough rounds an upper low over the northern
    Ontario/Quebec border this morning, tracking over the Great Lakes
    today, taking on a negative tilt as it crosses New England
    tonight. This will drive strengthening height falls and downstream
    PVA, collocated with the left exit of a modest pivoting jet streak
    within the pinched flow southeast of the amplifying trough. This
    will result in an intensifying surface low out of eastern New
    England this evening. The 00Z consensus is for the track to be a
    bit farther east which brings the cold enough atmospheric column
    for snow farther east, expanding the area of heavy snow over Maine.
    Day 1.5 PWPF for >6" is 40-80% over all but coastal and far
    southern Maine as well as the White Mountains and northern NH and
    the Northeast Kingdom of VT.

    Additionally, the associated strong cold front will race across
    Upstate NY through this afternoon. Along this front, CAMs remain
    in good agreement that waves of snow showers will occur, especially
    from northern PA/central NY into western New England this
    afternoon into this evening. The snow squall parameter lights up
    across this area, driven by 200-400 SBCAPE overlapped with 0-2km
    theta-e lapse rates falling well below 0C/km and high low- level
    RH. This suggests that at least scattered snow squalls will occur,
    with briefly heavy snow rates and gusty winds resulting in
    hazardous travel.

    ...Northern Rockies through the Upper Midwest and Great Lakes...
    Days 2-3...

    A stationary front persists over the northern High Plains through
    Thursday while intensifying cyclonic flow begins to envelop the
    northern Rockies through northern Plains south of an amplifying
    closed low over Manitoba. A notable impulse from off the PacNW
    today will shift east in zonal flow before getting caught in this
    cyclonic flow over northwest MT early Thursday which then drives
    surface cyclogenesis along the stalled front and a focused/
    progressive wave that shifts from western Nebraska late Thursday to
    the southern Great Lakes by late Friday. Ascent will be aided by
    the right entrance region of a modest/backing jet near the
    US/Canadian border and PVA from the mid-level impulse. This ascent
    atop the baroclinic gradient/surface low will drive a west to east
    oriented band of precipitation beneath the jet streak that will be
    met with Gulf-sourced moisture streaming up the Plains over the
    Dakotas late Thursday. An expanding precipitation shield northeast
    of the developing low is expected as the low approaches the Upper
    Midwest Thursday night. The low then shears/weakens into an
    inverted trough over the Midwest Friday, but synoptic dynamics
    remain strong as the cyclonic flow centered over southern Hudson
    Bay increases with plenty of Gulf moisture available. More marginal
    thermal conditions accompany the trough over the eastern Great
    Lakes Friday night, but the expansive precip shield extends into
    the cold enough thermals of the northern Great Lakes.

    The heaviest snow is expected around Glacier NP where increasing
    surface ridging out of the Canadian Prairies drives flow with an
    eastern component upslope into this area with the impulse passage
    early Thursday further aiding development/ascent.

    Day 2 PWPF for >6" is 80-100% in the Lewis Range of Glacier NP with
    stripes of 20-40% values from banding over southern ND into west-
    central MN. Day 2.5 PWPF for >6" is when values are most expansive
    with 30-70% values over much of WI and the northern half of the
    L.P. of MI. The focus thereafter is farther north of the trough
    axis and generally over southern Ontario, but the snow bands reach
    the eastern Great Lakes late Friday with Day 3 PWPF for >6" 20-50%
    over the Tug Hill and Adirondacks and north over the rest of NY
    from there.

    Back over the northern Rockies, the Day 3 PWPF for >6" are 20-50%
    for all of the Northwest MT ranges as the baroclinic zone in the
    immediate lee persists with mid-level Pacific moisture increasing
    as the ridge axis just west pivots south as the Hudson Bay low
    continues to amplify, keeping snow going over the northern Rockies.

    Day 3...

    Upper low currently on the northern BC coast shifts southwest
    through Thursday, phasing with other shortwave troughs to form a
    deeper closed low off the OR coast downstream of a potent omega
    high over eastern AK. This low then makes a wobbly approach to the
    OR coast Friday as an occluded low that then stalls near the coast
    until a reinforcing trough later in the weekend. A subtropical
    moisture feed is directed in from the southwest, working its way
    south over the entire state of CA late Friday through Saturday.
    Snow levels in this feed look to be 6000-7000ft though levels drop
    to 4000-5000ft over the Shasta/Siskiyou and Sierra Nevada Saturday
    under height falls where Day 3 PWPF for >8" are 50-80%. Wintry
    precip likely continues over these areas through Sunday under upper


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

    -- Winter storm becoming likely:
    Confidence is increasing that a large storm system will produce a
    swath of heavy snow, as well as freezing rain and sleet, across
    portions of the Northern Plains and Upper Midwest into early next

    -- Widespread heavy snow:
    Heavy snow will likely overspread eastern Montana late Saturday,
    then expand into the Northern Plains and Upper Midwest by Sunday
    night. Significant accumulations are likely. 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, could result in 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

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