• MESO: Mesoscale Discussion 1339

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Jul 24 15:45:12 2021
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    ACUS11 KWNS 241545
    SPC MCD 241544=20

    Mesoscale Discussion 1339
    NWS Storm Prediction Center Norman OK
    1044 AM CDT Sat Jul 24 2021

    Areas affected...Parts of central/northern lower Michigan

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

    Valid 241544Z - 241815Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Strong thunderstorms may begin developing by 2-4 PM EDT,
    particularly near and southwest through south of the Houghton Lake
    vicinity, where a supercell or two posing a risk for a tornado is
    possible initially, before strong wind gusts become the more
    prominent potential hazard.

    DISCUSSION...Near the base of large-scale mid-level troughing
    primarily shifting east of the Canadian Prairies into the Hudson Bay/northwestern Ontario vicinity, a southwesterly to westerly
    lower/mid tropospheric jet streak is in the process of propagating
    across the Upper Midwest and Great Lakes vicinity. This includes
    speeds on the order of 30-50+ kt in the 850-500 mb layer, with a
    couple of associated mid-level cyclonic vorticity maxima. One is
    migrating across and east-northeast of the Houghton Lake area, with
    another trailing to the west-southwest (now southeast of Oshkosh,
    WI). It appears that forcing for ascent with the trailing
    perturbation may begin impacting areas near/southwest through south
    of Houghton Lake, and northwest of Saginaw, as early as the 17-19Z
    time frame.

    Along a diffuse warm frontal zone across the region, a seasonably
    moist boundary layer, with surface dew points near 70F, appears
    characterized by CAPE on the order of 1000 J/kg. Mid-levels are
    relatively warm, but lapse rates still appear modestly steep, and at
    least some gradual boundary-layer warming may contribute to a
    further increase in CAPE through mid afternoon.

    Given the moderately strong deep-layer shear (including sizable clockwise-curved low-level hodographs), the increasing instability
    and forcing for ascent may become conducive to the development of
    organized convective development by mid afternoon. Isolated
    supercells posing at least some risk for a tornado or two may be
    possible initially, before activity tends to grow upscale with
    potentially damaging wind gusts becoming a more prominent hazard as
    activity spreads eastward.

    ..Kerr/Hart.. 07/24/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!vYmMGkS3ojPZyF2MndFtquCe2hytsvDJNvgW8Wl9l1e-JJNTTvFVxSrXi1T5_vWpwquYzswc$=
    for graphic product...


    LAT...LON 45108473 44968330 44038299 43178515 44078592 45108473=20

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