• MESO: Mesoscale Discussion 1771

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Sep 20 22:52:25 2021
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    ACUS11 KWNS 202252
    SWOMCD
    SPC MCD 202252=20
    WIZ000-MIZ000-IAZ000-MNZ000-MOZ000-210045-

    Mesoscale Discussion 1771
    NWS Storm Prediction Center Norman OK
    0552 PM CDT Mon Sep 20 2021

    Areas affected...Far southeast Minnesota...eastern Iowa...and
    western to northern Wisconsin

    Concerning...Severe Thunderstorm Watch 507...509...

    Valid 202252Z - 210045Z

    The severe weather threat for Severe Thunderstorm Watch 507, 509
    continues.

    SUMMARY...The threat for severe wind, and perhaps a brief tornado,
    continues across parts of the upper Mississippi River valley. The
    greatest severe risk may reside across west-central and northern
    Wisconsin over the next 2 hours.

    DISCUSSION...GOES IR imagery over the past two hours has shown a
    general cooling trend in convective cloud tops, indicative of
    intensifying storms. This trend has manifest at the surface in the
    form of a few severe wind reports from northeast IA within the past
    hour. An upstream mid-level speed max is noted in recent RAP
    analyses and water-vapor imagery, suggesting that deep-layer shear
    may improve over the next few hours and aid in further strengthening
    prior to the onset of diurnal cooling near sunset. As such, the
    severe threat will likely continue for at least the next 1-2 hours.=20


    A broken line of somewhat organized cells is beginning to congeal
    into a more cohesive line across far southeast MN, northeast IA, and
    western WI, which may evolve into a more organized wind threat
    during this 1-2 hour window. Nearly 40 knot 0-3 km bulk shear
    vectors and over 250 m2/s2 0-1 km SRH noted in the KARX VWP suggest
    the environment remains supportive of some tornado potential, though
    the orientation of the bulk shear vectors with the evolving
    line/cold front are not overly ideal for a robust QLCS tornado
    threat. Further north, shear vectors remain slightly stronger and
    are more favorably aligned with a balanced QLCS along the front. A
    few circulations have been noted from the KDLH radar, suggesting a
    heightened tornado potential for northern WI. This threat should
    persist through the remainder of the evening hours before diurnal
    cooling and stabilization occurs.

    ..Moore.. 09/20/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qUVRbVOEFqssl2IlaeFwV5GActASmhAPMbdzRiD3Xbbk0cFYW6eBU0cfG9xO2VL8TymlTlTn$=
    for graphic product...

    ATTN...WFO...MQT...GRB...MKX...DVN...DLH...ARX...MPX...DMX...
    EAX...

    LAT...LON 45469222 46359196 46729099 46418996 45528964 43929008
    42659070 41119180 40669239 40549303 40629388 41029397
    42209306 43599234 44469219 45469222=20



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