• MESO: Mesoscale Discussion 2056

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Dec 25 10:44:58 2021
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    ACUS11 KWNS 251044
    SWOMCD
    SPC MCD 251044=20
    MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-251545-

    Mesoscale Discussion 2056
    NWS Storm Prediction Center Norman OK
    0444 AM CST Sat Dec 25 2021

    Areas affected...portions of northeastern and extreme eastern NY...VT...central/southern NH...extreme southwestern ME...MA except southeastern areas...northern parts of CT/RI.

    Concerning...Winter mixed precipitation=20

    Valid 251044Z - 251545Z

    SUMMARY...A mix of winter precip will pass over northeastern NY and
    much of central/western New England through the remainder of the
    morning. This mostly will involve a transition from light snow to
    freezing rain to rain. Freezing rain rates of 0.05 to 0.15
    inches/hour are possible for 2-3 hours in some locales, before the
    precip transitions to all rain.

    DISCUSSION...Moisture-channel imagery indicates a shortwave trough
    moving rapidly east-northeastward across the IL/IN area and lower
    Ohio Valley, ahead of which a broad low-level warm-advection and moisture-transport plume extends across much of the Northeast. This corresponds to the northern branch of a two-pronged LLJ in the
    eastern CONUS, with that northern branch extending across PA and
    over parts of New England, per regional VWP data. An area of precip
    that has developed in the regime of large-scale lift will shift
    eastward to east-northeastward across the discussion area before the
    boundary layer warms above 32 F. Expect mainly light (locally/
    briefly heavier) and patchy snow on the leading edges, transitioning
    to freezing rain within roughly 1-2 hours, then rain 2-3 hours
    later.=20=20

    The bulk of hazardous winter precip should fall as freezing rain,
    with time series of forecast soundings reasonably showing a
    supportive superfreezing warm nose developing above the shallow/
    near-surface subfreezing layer. This process already is evident
    across much of eastern NY, with light freezing rain reported at
    several stations. The thickening warm layer will melt progressively
    greater snow amounts generated in a much-higher, essentially
    saturated dendritic-growth layer (centered between 500-550 mb), with
    saturated conditions extending to the surface a couple hours before freezing-rain/rain transition is complete. Continued warm advection
    will extend into the boundary layer with time, and from west to
    east, through mid/late morning. As this occurs, surface and
    near-surface temperatures will exceed 32 F, ending the freezing-rain
    episode.

    ..Edwards.. 12/25/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!tNQA2bRyNIQpm3N-3YVqRXTvVxgkhsdUYdBZiAe_ZNW09CT1NbpYkAaARdAHk7b5MkEPfqXk$=
    for graphic product...

    ATTN...WFO...GYX...BOX...BTV...ALY...

    LAT...LON 44997238 44557209 44167145 43557070 43127056 42917082
    42717075 42707068 42717059 42647059 42597071 42547084
    42407096 42327096 42297087 42277075 42007063 41997067
    41967051 41787175 42227334 43087366 43887465 44617446
    44987411 44997238=20



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