• MESO: Mesoscale Discussion 1492

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thu Aug 12 00:36:05 2021
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    ACUS11 KWNS 120036
    SWOMCD
    SPC MCD 120035=20
    MIZ000-INZ000-ILZ000-WIZ000-IAZ000-120200-

    Mesoscale Discussion 1492
    NWS Storm Prediction Center Norman OK
    0735 PM CDT Wed Aug 11 2021

    Areas affected...Eastern IA...Northern IL...Far Southern
    WI...Northwest IN...Southwest Lower MI

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

    Valid 120035Z - 120200Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Storm coverage is expected to increase this evening, with
    at least an isolated severe threat into late tonight. New watch
    issuance is possible by 01-02Z.

    DISCUSSION...Earlier supercells over eastern IA, southwest WI, and
    northwest IL have weakened over the last hour, likely due to
    generally weak large-scale ascent and modest capping noted in 00Z
    DVN sounding. However, regional soundings and VWPs also depict a
    rather strong southwesterly low-level jet across the area, which is
    generally forecast to intensify further tonight as it veers to a
    more westerly direction. Storm coverage is expected to increase with
    time later this evening within this warm advection regime, as
    airmass recovery continues across northern IL/IN and a surface
    boundary moves southeastward across the region.=20

    Even if storms remain somewhat elevated tonight, steep midlevel
    lapse rates and rich low-level moisture will still support large
    MUCAPE, with sufficient deep-layer shear for some organized storm
    structures. A mix of cells and clusters will be possible, posing a
    threat of at least isolated hail and damaging wind. A conditional
    tornado threat will also be present with any storm that can become
    rooted in the boundary layer, which would be most likely for a few
    hours this evening before MLCINH becomes increasingly prohibitive
    late tonight.=20

    While some uncertainty remains regarding the convective evolution
    and coverage of the severe threat later tonight, watch issuance is
    possible by 01-02Z, in advance of the expected increase in storm
    coverage.

    ..Dean/Goss.. 08/12/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!py11vXOq_ZW0waLoZJoz-SiFV23rLfSLYj8ZktbfT97DPQSQeHukhYC4Qxfvpy6CDO6n-7w7$=
    for graphic product...

    ATTN...WFO...IWX...GRR...LOT...ILX...MKX...DVN...

    LAT...LON 42149072 42459001 42748844 42788754 42408622 41758578
    40968857 40739068 41069116 41759107 42149072=20



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