• Winter Storm - US Rockies

    From Dumas Walker@1337:3/103 to All on Friday, November 08, 2024 09:16:00
    FOUS11 KWBC 080737
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    237 AM EST Fri Nov 8 2024

    Valid 12Z Fri Nov 08 2024 - 12Z Mon Nov 11 2024


    ...Central/Southern Rockies and Adjacent High Plains...
    Days 1-2...

    ...Heavy snow and major impacts continue for the Southern
    Rockies and Interstate 25 corridor into Saturday morning...

    Significant winter storm will persist across eastern CO through
    very early Saturday morning before ending. The primary driver of
    this impressive system is an anomalous upper low which will be
    moving across New Mexico this morning before slowly ejecting to the
    northeast and into the Central Plains on Saturday. NAEFS height
    anomalies reach as low as -3 sigma, indicating the strength of this
    feature, and the resultant downstream height falls and divergence
    will combine with a modestly coupled jet structure to produce
    impressive large-scale ascent across the Southern/Central Rockies
    and High Plains.

    This evolution today will also drive surface low development over
    Texas, and this wave will lift northward into Saturday. This low
    will be accompanied by enhanced forcing through persistent moist
    isentropic lift, especially along the 295K surface where mixing
    ratios climb to 4-6 g/kg, lifting into a robust TROWAL pivoting
    over the region Friday aftn/eve. Additionally, an axis of elevated
    instability is likely beneath the TROWAL and collocated with an
    axis of deformation, which suggests intense snowfall rates within a
    pivoting band of snowfall. Omega maxima into the DGZ, although
    subjectively elevated, will support heavy snow rates which the WPC
    snowband tool indicates will reach 1-2"/hr. It is possible that
    some rates may briefly even reach 2-3"/hr as model cross-sections
    indicate a narrow corridor of theta-es lapse rates <0C/km
    collocated with EPV<0 suggesting the potential for upright
    convection. Regardless, a highly impactful snow is expected again
    Friday from far northeast NM into much of eastern CO.

    The heaviest accumulations are likely in the higher elevations of
    the Raton Mesa, Palmer Divide, and into the Sangre de
    Cristos/southern Front Range, but intense ascent should allow for
    snow significant snow accumulations even into the High Plains, at
    least until the more intense easterly/WAA develops warming the
    column. There will likely be a thermal gradient near the KS/CO
    border which will be the demarcation between primarily snow and
    primarily rain, but even all the way to the KS border periods of
    snow are possible during heavier snow and dynamic cooling.
    WPC probabilities for more than 8 inches of additional snow on D1
    are above 80% across the Raton Mesa and Palmer Divide, as well as
    into the Sangre de Cristos and southern Front Range. Elsewhere,
    probabilities for more than 4 inches are high across much of
    eastern CO except towards the KS border and northeast corner.

    As the low occludes and shifts over Neb Friday night/Saturday, the
    moisture moisture fetch is shunted east and thermals farther east
    do not support snow, so the heavy snow threat generally ends in CO.
    Some lingering snowfall is likely, however, especially in the CO
    Rockies, but additional accumulations will likely be minimal.


    The probability of significant ice across the CONUS is less than
    10 percent.


    Weiss


    ...Winter Storm Key Messages are in effect. Please see current
    Key Messages below...

    https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

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