• MESO: Mesoscale Discussion 1473

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tuesday, September 18, 2018 06:58:01
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    ACUS11 KWNS 180657
    SWOMCD
    SPC MCD 180657
    MNZ000-180930-

    Mesoscale Discussion 1473
    NWS Storm Prediction Center Norman OK
    0157 AM CDT Tue Sep 18 2018

    Areas affected...Central portions of MN including the western Twin
    Cities Metro

    Concerning...Severe potential...Watch unlikely

    Valid 180657Z - 180930Z

    Probability of Watch Issuance...5 percent

    SUMMARY...Isolated hail up to around 1 inch diameter will be
    possible into the early morning across a portion of central
    Minnesota, generally within a narrow corridor from Lac Qui Parle
    County to the western part of the Twin Cities Metro.

    DISCUSSION...Trends in mosaic radar imagery and MRMS MESH indicated
    periodic increases in reflectivity intensities and hail sizes,
    respectively, since 550Z within the discussion area. This corridor
    of storms is located within the apex of 25-30-kt southwesterly
    low-level jet extending from the central Plains to southwest/central
    MN, where warm advection is maximized well north of a surface front
    draped across IA into NE. Although any forcing aloft is likely weak
    to negligible, this warm advection is expected to support additional
    storms through the overnight into early this morning. The presence
    of steep midlevel lapse rates (7.5-8 C/km) extending east across the
    upper Mississippi Valley, moderate elevated instability and
    effective bulk shear of 30-40 kt suggest an environment favorable
    for large hail from storms rooted above the stable boundary layer.
    The low-level jet is expected to veer to westerly by 12Z and weaken,
    suggesting a gradual diminishing trend in the strength of the
    stronger elevated storms.

    ..Peters/Edwards.. 09/18/2018

    ...Please see www.spc.noaa.gov for graphic product...

    ATTN...WFO...MPX...

    LAT...LON 45139597 45279528 45249386 45169329 44859321 44719347
    44639452 44729556 44759588 44979608 45139597



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