• MESO: Mesoscale Discussion 1946

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Nov 13 19:06:58 2021
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    ACUS11 KWNS 131906
    SPC MCD 131906=20

    Mesoscale Discussion 1946
    NWS Storm Prediction Center Norman OK
    0106 PM CST Sat Nov 13 2021

    Areas affected...Parts of central into eastern Massachusetts...Connecticut...Rhode Island...and Long Island

    Concerning...Severe Thunderstorm Watch 549...

    Valid 131906Z - 132030Z

    The severe weather threat for Severe Thunderstorm Watch 549

    SUMMARY...The risk for potentially damaging wind gusts seems likely
    to increase through 3-5 PM EST, in association with an eastward
    advancing band of showers and thunderstorms across Long Island and
    Connecticut into parts of central and eastern Massachusetts and
    Rhode Island.

    DISCUSSION...Pre-frontal boundary-layer destabilization remains
    largely driven by steepening low-level lapse rates due to insolation
    and mixing. Due to the mixing, surface dew points actually have
    fallen a couple of degrees across most areas, and range from the mid
    30s to mid 40s F across all but Long Island into far southern
    Connecticut, where they are near 50F. Still, the eastward
    progression of mid-level cooling due to cold advection and lift
    should be sufficient to maintain the narrow band of low-topped
    thunderstorms focused along and to the northwest of the 100+ kt
    southwesterly offshore 500 mb speed maximum.

    Two hourly surface pressure falls on the order of 3-4 mb were
    evident in 18Z observations along a corridor from the New Jersey
    coast through the Concord, NH vicinity, and are likely to be
    accompanied by strengthening of southerly low-level flow during the
    next few hours. The latest Rapid Refresh suggests that this may
    include speeds in excess of 40 kt around the 850 mb level across
    eastern Long Island into eastern Massachusetts by 21-22Z. Coupled
    with further steepening of low-level lapse, downward mixing of
    higher momentum probably will contribute to increasing risk for
    potentially damaging wind gusts.

    ..Kerr.. 11/13/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oN7qRVp7kQUhvppohAhrbsrv3M_hTGRvRC2p5_G_frdIlh04uAryCVNVjWEs8fgCQ8ELOzBQ$=
    for graphic product...


    LAT...LON 42637232 42167140 40877193 40557281 40067391 40547384
    41277321 41927287 42637232=20

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