• MESO: Mesoscale Discussion 1945

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Nov 13 17:07:27 2021
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    ACUS11 KWNS 131707
    SPC MCD 131707=20

    Mesoscale Discussion 1945
    NWS Storm Prediction Center Norman OK
    1107 AM CST Sat Nov 13 2021

    Areas affected...Parts of New Jersey...southeastern New York...Long Island...Connecticut...Rhode Island and Massachusetts

    Concerning...Severe potential...Watch likely=20

    Valid 131707Z - 131900Z

    Probability of Watch Issuance...80 percent

    SUMMARY...Showers and thunderstorms are expected to intensify across
    the region, spreading from near northern Mid Atlantic coastal areas
    into southern New England, accompanied by increasing risk for
    potentially damaging wind gusts and perhaps a couple of tornadoes
    through late afternoon.

    DISCUSSION...Although details differ considerably among the various
    models, it seems probable that surface low pressure will begin to
    consolidate across parts of central New Jersey into the western Long
    Island vicinity by mid afternoon, before deepening while continuing
    to track east-northeastward across southeastern New England through
    22-00Z. This is expected in response to strengthening large-scale
    forcing for ascent, ahead of a vigorous short wave trough currently
    pivoting across the northern Virginia/central Maryland vicinity.

    It appears that this will include intensifying lift within a
    corridor along and ahead of an associated cold front, preceded by at
    least weak destabilization within an expanding warm sector across
    parts of southeastern New England. It is uncertain whether
    destabilization will be sufficient to support discrete storm
    development ahead of the east-northeastward surging cold front, but
    the evolution of at least a narrow line of low-topped convection
    seems probable in response to the enhanced mesoscale lift.

    Likely located along/just north of a belt of 70-90+ kt flow around
    the 500 mb level, cloud bearing layer shear will be quite strong and
    more than sufficient to contribute to organized convection with the
    potential to produce small hail and potentially damaging wind gusts.
    Low-level wind fields are initially relatively modest, with
    pre-frontal southerly 850 mb flow still around 30 kt, and this could
    slow the development of increasing potential for severe wind gusts.=20
    However, guidance generally indicates that substantive further
    strengthening of this flow to 40-50+ kt is possible, particularly by
    late afternoon across parts of eastern Long Island into southeastern
    New England, where enlarging low-level hodographs might become
    conducive to a risk for tornadoes, in addition to increasing
    potential for severe wind gusts.

    ..Kerr/Hart.. 11/13/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!owTkW6F329PXEa_YpI17jjrWAEDpJwQIE1yk-iU-v7Y6MyMK4QVWEzNsTSNFDBC1OctMWUkd$=
    for graphic product...


    LAT...LON 40777469 41367455 42337294 42307120 40817136 39797396
    39907475 40777469=20

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