• MESO: Mesoscale Discussion 1157

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Jul 5 22:45:01 2021
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    ACUS11 KWNS 052244
    SPC MCD 052244=20

    Mesoscale Discussion 1157
    NWS Storm Prediction Center Norman OK
    0544 PM CDT Mon Jul 05 2021

    Areas affected...Far southeast South Dakota into northwest Iowa

    Concerning...Severe potential...Watch unlikely=20

    Valid 052244Z - 060045Z

    Probability of Watch Issuance...5 percent

    SUMMARY...Thunderstorms may develop along a stationary boundary
    across northwest to north-central Iowa prior to sunset, though the
    potential for additional storms is uncertain. However, storms that
    do form could pose a brief severe hail risk.

    DISCUSSION...Recent satellite imagery continues to show a generally
    shallow cumulus field along a stationary boundary draped across
    northern IA. Despite the meager appearance of the cumulus field, new
    convection has been intensifying at the intersection of the boundary
    and convective outflow from an upstream cluster of storms across
    southeast SD. Although lift is locally augmented at this
    intersection, objective analysis trends over the past hour suggest=20 convergence may be gradually increasing along the stationary
    boundary across northwest IA, and RAP forecast soundings hint that
    low-level parcels are near their convective temperatures. This
    suggests that an isolated thunderstorm or two could develop either
    1) along the stationary boundary (likely prior to sunset and the
    onset of boundary-layer stabilization) or 2) along the convective
    outflow as it gradually pushes east through the evening hours.
    Confidence in either solution is somewhat low, and storm chances
    decrease with eastward extent due to weaker convergence/implied
    ascent. Given moderate instability in place (upwards of 3000 J/kg
    MLCAPE), any storms that do form may initially be capable of
    producing severe hail, though the lack of sufficient deep-layer
    shear will limit the duration of this threat. Given the lack of
    confidence in storm coverage and low potential for robust storm
    organization, a watch is not expected.

    ..Moore/Hart.. 07/05/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!pbQEJ0zjSTszvjDLGHQxKSXpbtTpQlf3jKgxKFEwDsn5YFt--t5RCtFJLvTYHjg76Yuo7eo5$=
    for graphic product...


    LAT...LON 43519755 43799713 43489638 43379539 43369469 43279407
    43099342 42579342 42389401 42569502 42639637 42699702
    42889763 43099788 43519755=20

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