• Significant winter storm

    From Dumas Walker@21:1/175 to All on Tuesday, April 02, 2024 07:47:00
    FOUS11 KWBC 020831

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    431 AM EDT Tue Apr 2 2024

    Valid 12Z Tue Apr 02 2024 - 12Z Fri Apr 05 2024

    ... Great Lakes into the Northeast... Days 1-3...

    ...Significant late season winter storm this week...

    A well-defined southern stream shortwave continues to lift
    northeast across the central Plains this morning. This system is
    expected to continue tracking northeast into the mid-to-upper
    Mississippi Valley and western Great Lakes region, where it will
    begin to interact with an equally defined northern stream trough
    diving out of central Canada. As the two streams phase, models
    show an upper low rapidly developing over the upper Mississippi
    Valley and western Great Lakes this afternoon and evening. Strong
    upper forcing overlapping low level frontogenesis will support rain
    quickly changing to heavy snow on the backside of the associated
    surface low as it tracks out of the mid Mississippi Valley toward
    the Great Lakes this afternoon and evening. HREF guidance shows
    heavy banded snow with rates of 1-2 inch/hour developing across
    southern Wisconsin by the late afternoon, before gradually
    expanding north into Upper Michigan during the evening into the
    overnight hours. Following a significant western shift in the
    guidance from the 00Z to the 12Z runs earlier today, the latest 00Z
    guidance has shown overall better run-to-run continuity. However,
    some models, including the GFS, continue trend west, raising
    probabilities for heavy snow further west across Wisconsin. Snow
    will continue to fall across the region through Wednesday, however
    overall rates are expected to diminish as the low begins to drop
    back to the southeast. A primary exception will likely be the
    central to western U.P., which will be the focus for strong
    easterly flow off of Lake Superior as the low meanders over
    southern Wisconsin on Wednesday before drifting southeast toward
    the Ohio Valley. WPC PWPF probabilities for snow accumulations of 8
    inches or more are above 70 percent from southern Wisconsin to the
    U.P. The highest probabilities are centered over the central U.P.,
    where the PWPF even shows some 50 percent or greater probabilities
    for 2 feet or more before the snow ends on Thursday.

    Meanwhile, additional southern stream energy phasing with the low
    will support the development of a triple-point low that will start
    to become the primary surface feature as it tracks from the Mid
    Atlantic to Long Island and southern New England late Wednesday
    into early Thursday. Precipitation will begin to spread across
    eastern New York into New England on Wednesday, with mixed
    precipitation at the onset for much of the interior. Low-to-mid
    level frontogenesis along with divergence aloft will support
    stronger ascent and a transition to snow across northern New York
    and interior central to northern New England. It is unclear how
    much an intrusion of dry air and warm air aloft may impact amounts. Probabilities for heavy snow have retreated a bit further to the
    north with latest run across from the Catskills eastward into
    central Massachusetts, southern Vermont and New Hampshire.
    Relatively lighter QPF and the potential for a more prolonged
    period of sleet are contributing to the lower probabilities.
    Heavy, wet snow still appears likely for at least portions of the
    Adirondack, Green, and White mountains. WPC PWPF shows high
    probabilities for 8 inches or more extending from these areas into
    central Maine. Snow will continue across the region into Friday,
    however rates should begin to diminish by late Thursday as the low
    lingers but weakens over New England.

    ...Western U.S.... Days 2-3...

    An amplified upper trough associated with a low dropping south from
    the Gulf of Alaska will begin to dig into the northwestern U.S. on
    Wednesday. Backing flow ahead of the advancing trough will support
    deepening moisture and the increasing potential for snow along a
    low-to-mid level front extending northeastward from the southern
    Cascades on Wednesday. While widespread heavy accumulations are
    not expected, locally heavy amounts are possible from the southern
    Cascades to the Blue Mountains late Wednesday into early Thursday.

    By early Thursday, models show a deep upper low centered along the
    Northwest coast that will then dig further south into northern
    California by early Friday. This will bring heavy snows into the
    Sierra Nevada and parts of central and northern Nevada. Meanwhile,
    energy lifting east of the low and a lingering frontal boundary
    will support additional heavy amounts across northeastern Oregon.
    For portions of the Sierra Nevada, southern Cascades, and the Blue
    Mountains, WPC PWPF shows high probabilities for 8 inches or more.


    *** Key Messages for Early April Nor'easter ***

    ---Long duration winter storm

    A large storm system will produce gusty winds and late-season
    heavy snow across portions of the Great Lakes and the Northeast
    beginning later today and continuing through midweek.

    ---Western Great Lakes heavy snow Tue night

    Heavy snow will likely develop over Wisconsin by this
    afternoon and expand into Upper Michigan overnight. Snow will
    continue over much of the region through Wednesday, with additional
    heavy snow across portions of Upper Michigan, before ending on

    ---Northeast snow and wind Wednesday-Friday

    Secondary low pressure development along the Mid-Atlantic coast
    will likely bring heavy, wet snow and some sleet to the Northeast
    Wednesday afternoon through Friday. Significant snow accumulations
    are likely over parts of northern New York and New England.

    ---Significant impacts from heavy snow and wind

    The combination of heavy snow rates and gusty winds will likely
    result in hazardous travel due to low visibility and snow-covered
    roads. The wet snow and high snow load may cause tree damage and
    impact infrastructure.

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