• MESO: Mesoscale Discussion 1728

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sun Sep 12 04:20:45 2021
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    ACUS11 KWNS 120420
    SPC MCD 120420=20

    Mesoscale Discussion 1728
    NWS Storm Prediction Center Norman OK
    1120 PM CDT Sat Sep 11 2021

    Areas affected...Parts of southeastern Minnesota into west central

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

    Valid 120420Z - 120615Z

    Probability of Watch Issuance...20 percent

    SUMMARY...The development of a few storms, with at least some
    potential to produce large hail, appears possible by 1-3 AM CDT, if
    not before. While the need for a watch still appears unlikely,
    trends will continue to be monitored.

    DISCUSSION...Westerly to northwesterly mid-level flow across much of
    the Upper Midwest is seasonably strong, but broadly confluent,
    downstream of a substantive short wave trough straddling the
    Montana/North Dakota international border area. However, at least a
    couple of much more subtle, lower amplitude perturbations are
    progressing through this regime, and may contribute to a developing
    area of strengthening large-scale ascent aided by lower/mid
    tropospheric warm advection.=20=20

    During the next few hours, it appears that this may become focused
    within a corridor generally north of the Rochester, MN and La Crosse
    WI areas. This is to the north/cool side of a slowly southward
    advancing surface cold front, where low-level moisture overrunning
    the front, beneath the northern periphery of very warm and capping
    elevated mixed-layer, appears to be contributing to sizable CAPE up
    to around 2000 J/kg.

    Latest model output varies concerning the extent to which mid-level
    inhibition may suppress thunderstorm development tonight, but given
    the potential instability and at least subtle signal for increasing
    lift in the mid-levels, there appears at least low probabilities for
    the initiation of storms. This may occur as early as 05-06Z, but
    it appears a bit more probable toward 07-08Z.

    Of primary concern, if storms do initiate, cloud-bearing layer shear
    profiles appear conducive to supercells which could pose a risk for
    sizable (perhaps greater than golf ball) hail.

    ..Kerr/Grams.. 09/12/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!v0FQY1a4EH_1HCio1s6KDiDqlsfStjg1DQNWl4LhoDurSNU53mOYAm6lmagAQiGcMNh3h5I0$=
    for graphic product...


    LAT...LON 44559262 44779039 43999000 43949101 43719258 44559262=20

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