• MESO: Mesoscale Discussion 1453

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Aug 9 22:53:52 2021
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    ACUS11 KWNS 092253
    SPC MCD 092253=20

    Mesoscale Discussion 1453
    NWS Storm Prediction Center Norman OK
    0553 PM CDT Mon Aug 09 2021

    Areas affected...Parts of northern Illinois

    Concerning...Tornado Watch 417...

    Valid 092253Z - 100000Z

    The severe weather threat for Tornado Watch 417 continues.

    SUMMARY...Vigorous thunderstorm development, including discrete
    supercell structures with the potential to produce relatively
    short-lived tornadoes, will continue into the 7-9 PM time frame.=20
    This could impact western and southwestern portions of the Greater
    Chicago metro area, before activity possibly consolidates into an
    organizing, southward and southwestward moving cluster.

    DISCUSSION...To the south of a weak surface low/low-level cyclonic
    circulation centered near/east of Madison, WI, a corridor of
    stronger low-level surface heating and confluent low-level flow will
    remain the focus for vigorous thunderstorm development into the
    evening hours. Mid-level temperatures above this corridor are
    relatively warm (including 500 mb temps around -6C), but
    boundary-layer moisture content is seasonably high, with surface dew
    points in the lower/mid 70s F.=20=20

    Beneath northwesterly mid-level flow (30-35+ kt around 500 mb) to
    the west of the mid-level trough axis, 30+ kt southwesterly flow
    around 850 mb along this corridor is contributing to sufficient
    shear for supercells. While the severe hail risk appears low, the
    high boundary-layer moisture content coupled with modest, clockwise
    curved low-level hodographs have been conducive to occasional brief
    tornadic development, and this may remain the case another hour or

    Into the 01-03Z time frame, at least some model output suggests that
    convection could begin to congeal into a small organizing cluster of
    storms near or to the west/southwest of the Greater Chicago area. If
    this occurs, stronger thunderstorm activity should tend propagate to
    the south and southwest, with at least some increase in potential
    for a strong downburst or two, while the risk for tornadoes

    ..Kerr.. 08/09/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!plhghU1ulOPO78ocschlpF8pdq47zoOOQLtM26B9710UAg93ldXAIuA9FKqp2ifoVn4oKZIt$=
    for graphic product...


    LAT...LON 41598991 42018904 42268860 42498798 42338771 41878746
    41268784 41088895 41268969 41598991=20

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