• MESO: Mesoscale Discussion 1450

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Aug 9 17:19:20 2021
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    ACUS11 KWNS 091719
    SWOMCD
    SPC MCD 091718=20
    INZ000-ILZ000-091945-

    Mesoscale Discussion 1450
    NWS Storm Prediction Center Norman OK
    1218 PM CDT Mon Aug 09 2021

    Areas affected...Portions of northern IL and extreme northwestern IN

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

    Valid 091718Z - 091945Z

    Probability of Watch Issuance...60 percent

    SUMMARY...A threat for large hail, damaging winds, and a couple of
    tornadoes should increase this afternoon. Watch issuance is
    possible.

    DISCUSSION...A well defined MCV is located over southern WI early
    this afternoon. Convection that has occurred through the morning
    across parts of northern IL on the southern flank of this feature is
    in the process of moving over the northern suburbs of Chicago and
    southern Lake Michigan. In the wake of this activity, modest diurnal
    heating of a moist low-level airmass, but muted by persistent
    low-level cloud cover, should support increasing instability by late
    afternoon. The development of 1500-3000 J/kg of MLCAPE still appears
    probable by 22-23Z along/south of the outflow left by the morning
    storms across northern IL. Recent VWPs from KLOT show southerly
    low-level winds veering and strengthening with height through mid
    levels, with around 30-40 kt of effective bulk shear present per
    mesoanalysis estimates. This should be enough to support a mix of
    supercells and multicells this afternoon as renewed convection
    develops across northern IL, with continued low-level warm advection
    atop the outflow boundary and ascent associated with the MCV
    providing lift. Large hail may occur with any supercell, and the
    potential for a couple tornadoes is also apparent with effective SRH
    around 150-250 m2/s2 across northern IL this afternoon and early
    evening owing to the presence of a 25-30 kt southwesterly low-level
    jet. A small cluster may eventually develop as storms move slowly south-southeastward off the boundary. If this occurs, then
    severe/damaging winds may eventually become this primary threat. The
    potential for surface-based storms should increase over the next
    couple of hours as surface temperatures warm into the low 80s, and
    watch issuance is being considered in this time frame.

    ..Gleason/Thompson.. 08/09/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oTtGHPclJFmQMZS9uOYJH6G30iljDiI7t097xBqp7Mq6xNt1VMHp5JWdx08NpYdPD9JRlGSF$=
    for graphic product...

    ATTN...WFO...LOT...DVN...

    LAT...LON 41828994 42198997 42468933 42458773 41608695 41058708
    41018866 41418949 41828994=20



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