• MESO: Mesoscale Discussion 1427

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Aug 7 02:10:35 2021
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    ACUS11 KWNS 070210
    SWOMCD
    SPC MCD 070209=20
    SDZ000-NEZ000-070415-

    Mesoscale Discussion 1427
    NWS Storm Prediction Center Norman OK
    0909 PM CDT Fri Aug 06 2021

    Areas affected...Parts of southern South Dakota and adjacent
    northern Nebraska

    Concerning...Severe Thunderstorm Watch 410...

    Valid 070209Z - 070415Z

    The severe weather threat for Severe Thunderstorm Watch 410
    continues.

    SUMMARY...Rapidly intensifying thunderstorm activity with increasing organization and the potential to produce severe wind gusts appears
    possible through 11 PM-1 AM CDT. Trends are being monitored for the possibility of an additional severe weather watch east of WW 410.

    DISCUSSION...Convection appears to have generated a fairly
    significant surface cold pool, with 4-6 mb 2 hourly pressure rises
    evident in 01Z surface observations at Rapid City, SD and Chadron,
    NE. As this cold pool advances eastward along the remnant zone of
    stronger daytime differential surface heating/boundary-layer mixing, thunderstorm activity continues to increase and intensify along its
    leading edge. This includes areas as far north as the Interstate 90
    corridor, west of Philip, SD, but strongest storm development may be
    maintained near the southern flank of the cold pool, near the South Dakota/Nebraska border vicinity. This is roughly along the
    northeastern edge of the warmer and more strongly capping elevated
    mixed-layer air, which extends eastward into the Sioux Falls/Sioux
    City area of the mid Missouri Valley.

    During the past few hours, surface dew points have increased from
    60-65F at Valentine, NE, where temperatures remain in the upper 80s
    F. This has been aided by advection on easterly near surface flow,
    with dew points as high as the lower/mid 70s at Yankton, SD and
    Sioux City, IA, where the nose of a nocturnally strengthening
    southerly low-level jet (30-40 kt at 850) is forecast to become
    focused by 06Z.

    As eastward advancing convection encounters increasingly moist
    inflow characterized by large CAPE in excess of 3000 J/kg, there
    appears potential for substantive intensification and upscale
    growth. With easterly low-level flow contributing to strong
    deep-layer shear on the order of 40-50 kt, if this occurs, activity
    likely will become increasingly organized with the risk for severe
    wind gusts increasing once again, aided by steep lower/mid
    tropospheric lapse rates.

    ..Kerr.. 08/07/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oXlKDHkZAfv4v1PF6OrQ0fwY5ILVFNKzERDpenarWtWtMB6IBXE_iORLi2K35y-__ITag_tG$=
    for graphic product...

    ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

    LAT...LON 44000070 44259959 44309759 44119690 43549667 42549711
    42669814 42789904 42790012 42930051 43490083 44000070=20



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