• MESO: Mesoscale Discussion 1617

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Aug 27 18:53:20 2021
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    ACUS11 KWNS 271853
    SWOMCD
    SPC MCD 271853=20
    IAZ000-MNZ000-272030-

    Mesoscale Discussion 1617
    NWS Storm Prediction Center Norman OK
    0153 PM CDT Fri Aug 27 2021

    Areas affected...North Central Iowa and Southern Minnesota

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

    Valid 271853Z - 272030Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Ongoing storms may become surface based in the next 1-3
    hours and increase the severe threat. Area is being monitored for
    possible watch issuance.

    DISCUSSION...Visible satellite shows widespread cloud cover over
    parts of northern Iowa and southern Minnesota associated with
    renewed convective development. This is in response to ascent from
    an approaching mid-level shortwave trough and low-level warm/moist
    air advection. Peripheral/adjacent areas of this activity have
    warmed into the mid 80s F to low 90s F where strong insolation has
    been occurring this morning and early afternoon. With rich low-level
    moisture in place (70+ F surface dew point temperatures), a corridor
    of moderate instability (MLCAPE near 2500 J/kg) has developed across west-central and central Iowa amid ample deep-layer shear (effective
    bulk shear 35-45 kt).

    The short-term evolution of the ongoing convective activity and any
    new development remains unclear. With the aforementioned downstream
    heating and destabilization that is occurring, it seems plausible
    for the activity over north-central Iowa to become surface-based in
    the next couple of hours. This scenario is supported by
    high-resolution satellite imagery showing boundary-layer cumulus
    developing along the southeastern flank of this activity along an
    apparent surface trough. Should this occur, storms may quickly
    acquire supercell characteristics. Surface winds remain backed
    across north-central Iowa, supporting a favorable low-level shear
    environment (e.g., 0-3 km SRH 300 m^2/s^2) for a tornado risk, in
    addition to large hail and damaging winds.

    Although cloud cover remains expansive farther north, over parts of
    southern Minnesota, continued low-level warm/moist advection and
    possible clearing along with ascent from the advancing mid-level
    trough may allow for additional convective development later this
    afternoon. These areas continue to be monitored for potential watch
    issuance.

    ..Karstens/Dial.. 08/27/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!r9PAYfpOtqnJEXUHqr07VERHNBeHthH6dwZyHNrclTat9iMsynFGhESt61yvrKzyPNQgGryw$=
    for graphic product...

    ATTN...WFO...DVN...ARX...MPX...DMX...

    LAT...LON 42139334 42319471 43119490 44029407 44169290 43709155
    42929141 42469215 42139334=20



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