• MESO: Mesoscale Discussion 1765

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Sep 17 05:53:56 2021
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    ACUS11 KWNS 170553
    SPC MCD 170553=20

    Mesoscale Discussion 1765
    NWS Storm Prediction Center Norman OK
    1253 AM CDT Fri Sep 17 2021

    Areas affected...southern MN...northwest IA

    Concerning...Severe potential...Watch possible=20

    Valid 170553Z - 170700Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Strong to locally severe gusts are possible as a squall
    line moves east across southern MN.

    DISCUSSION...Latest surface mesoanalysis places a pre-frontal
    boundary oriented from southwest MN northeastward into parts of
    central MN ahead of a squall line advancing east. The surface wind
    shift will probably continue to serve as a focus area for the
    northern periphery of stronger outflow winds. South of the
    boundary, surface temperatures are warmer with low-mid 70s observed.
    The Sioux Falls, SD 88D VAD showed a strong southwesterly LLJ this
    evening (50+ kt) beneath a weakness in flow evident in the hodograph
    in the 3-6 km AGL layer, surmounted by stronger flow above (50-65 kt
    in the 6-9 km layer). This wind profile undoubtedly favors a squall
    line mode. It appears the orientation of the squall line is at
    least marginally favorable with respect to the mean flow in the 1-6
    km layer. So despite appreciable convective inhibition from a
    slow-to-cool boundary layer, the strength of the wind field may
    continue to enable localized severe gusts with the squall line. A
    plethora of surface observations during the past hour seem support
    this notion (e.g., KFSD, KPQN, KBKX) with gusts ranging mainly in
    the 40-45 kt range.

    ..Smith/Guyer.. 09/17/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!rjVuIKtzLgl0APhp38AbhqN6MUBicYPBCaGG6jip8ofFyJZrixZzDdp5G7o3kc_vJ0RGXih7$=
    for graphic product...


    LAT...LON 45259369 44569570 43659589 42819651 43079496 43499342
    44169286 45029294 45259369=20

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