• MESO: Mesoscale Discussion 1832

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Oct 11 17:38:02 2021
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    ACUS11 KWNS 111737
    SPC MCD 111737=20

    Mesoscale Discussion 1832
    NWS Storm Prediction Center Norman OK
    1237 PM CDT Mon Oct 11 2021

    Areas affected...portions of north-central IL...eastern WI and
    northwestern MI

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

    Valid 111737Z - 111930Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Ongoing convection ahead of the upper low may pose a risk
    for damaging winds and perhaps a brief tornado through much of the
    afternoon. However, cloud cover and stratiform rain cast
    considerable uncertainty on the convective evolution.

    DISCUSSION...As of 1715 UTC, a well-defined upper low was located
    near the Mississippi river along the border of MO and IL. To the
    east, remnant convection and precipitation were ongoing across much
    of central and northern IL. Despite dense cloud cover, low-level
    warm advection ahead of the upper low has warmed surface
    temperatures into the low to mid 70s as far north as the IL WI
    border. With low-level moisture in place (mid 60s F surface
    dewpoints) SPC mesoanalysis shows weak buoyancy (MLCAPE of 500-1000
    J/kg) has developed. Continued low-level advection and the arrival
    of strong dynamic lift ahead of a jet streak around the base of the
    upper low may support some additional destabilization, though the
    magnitude remains uncertain. The strong ascent timed with the
    arrival of the upper jet will also support very strong shear
    profiles across much of the upper Midwest and Great Lakes. Regional
    model sounding and VWPs showing 0-6 km shear of 50-60 kts with
    backed low-level flow also supporting large low-level hodographs.
    Thus, supercells would be the expected storm mode with a risk for
    damaging winds, hail, and perhaps a tornado or two.=20

    Convective evolution of the ongoing cluster of storms across
    north-central IL remains highly uncertain given the lack of stronger
    buoyancy and continued development of showers and thunderstorms
    ahead of the best kinematic environment northeast of the upper low.
    While several weakly rotating embedded elements have been observed
    over the last hour in central IL, the lack of greater buoyancy may
    result in poor storm organization this afternoon. Strong low-level
    shear (0-1 srh 200-300 m2/s2) and forcing will more than likely
    support some severe risk, through the evolution maybe very gradual
    and limited spatially.=20

    Farther downstream across portions of northern lower MI, greater
    clearing will likely support better buoyancy through much of the
    afternoon. Somewhat removed from the better dynamics of the upper
    low, a few strong/severe storms, including a supercell, may develop
    with a risk mainly for damaging winds. Despite the better buoyancy,
    the stronger flow aloft and better shear are forecast to arrive
    later in the diurnal cycle poorly timed with destabilization. As
    such, confidence also remains low on severe weather potential.
    Trends are being monitored for a possible weather watch though
    overall uncertainty remains very high.

    ..Lyons/Hart.. 10/11/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oNjXWcWyJ0f5aG1gFRRv1P3DzroRKTnJoXnM4yyGk5eZ1FQE_qSz_ImN45CmkiBVkRF019h6$=
    for graphic product...


    LAT...LON 43378880 44758718 45408578 45328511 44838441 44068494
    42898648 41978722 41308775 40798810 40528883 40708955
    41199045 41799017 42178982 43378880=20

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