• MESO: Mesoscale Discussion 1430

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Aug 7 16:04:41 2021
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    ACUS11 KWNS 071604
    SPC MCD 071603=20

    Mesoscale Discussion 1430
    NWS Storm Prediction Center Norman OK
    1103 AM CDT Sat Aug 07 2021

    Areas affected...Portions of southeastern MN...northeastern IA...and
    western WI

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

    Valid 071603Z - 071830Z

    Probability of Watch Issuance...40 percent

    SUMMARY...A threat for large hail, damaging wind gusts, and perhaps
    a few tornadoes may increase through the early afternoon. Watch
    issuance is possible.

    DISCUSSION...Recent visible satellite and radar imagery clearly
    shows a MCV moving quickly eastward across MN and towards
    west-central WI late this morning. On the southern flank of this
    feature, a 25-35 kt southwesterly low-level jet has encouraged a
    recent uptick in convection across southeastern MN and northeastern
    IA. It appears that this activity is mainly elevated at the moment,
    with a weak front/outflow boundary located over southern MN. Still,
    with around 35-40 kt of deep-layer shear present, any elevated
    supercells may pose an isolated threat for primarily large hail in
    the short term. Storms may eventually transition to surface-based
    over the next few hours, particularly along and south of the
    convectively reinforced boundary over southern MN.

    A rich low-level airmass characterized by at least low 70s surface
    dewpoints is present across much of IA into southern MN. Both
    diurnal heating of this airmass and the presence of steep mid-level
    lapse will likely contribute to around 2000-3000 J/kg of MLCAPE this
    afternoon. In addition to the large hail threat with any supercells,
    damaging winds may also occur if storms can congeal into one or more
    clusters and then move east-southeastward along the surface boundary
    into western WI. 25-35 kt of southwesterly winds in the boundary
    layer and a veering wind profile with height should support 100-200
    m2/s2 of 0-1 km SRH, sufficient for updraft rotation and a threat
    for a few tornadoes. This tornado threat will probably be maximized
    near the surface boundary across parts of southern MN into far
    northeastern IA and southwestern WI. Convective trends will be
    closely monitored for possible watch issuance in the next few hours.

    ..Gleason/Thompson.. 08/07/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!vnUfJzPYyVNN7UVxHvIQ-zgPNyxFG25r4JwUVmS5v-ADG2A1-CWBwJUXlXmGeLl_E7OOsB1Q$=
    for graphic product...


    LAT...LON 43548995 42998986 42689018 42539067 42409221 42669321
    42949368 43929391 44389282 44439206 44209109 43548995=20

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