• MESO: Mesoscale Discussion 1017

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Jun 19 21:59:01 2021
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    ACUS11 KWNS 192158
    SWOMCD
    SPC MCD 192158=20
    SDZ000-NEZ000-NDZ000-MTZ000-WYZ000-192330-

    Mesoscale Discussion 1017
    NWS Storm Prediction Center Norman OK
    0458 PM CDT Sat Jun 19 2021

    Areas affected...Southeastern Montana...northeast Wyoming...and
    portions of the Dakotas.

    Concerning...Severe potential...Watch unlikely=20

    Valid 192158Z - 192330Z

    Probability of Watch Issuance...20 percent

    SUMMARY...Storm initiation appears possible in the next 1 to 2 hours
    across the central and northern High Plains. A narrow corridor of
    buoyancy will support a few hours of isolated severe potential with
    high-based storms. Uncertainty on storm coverage and severity
    remains high.

    DISCUSSION...Ahead of a deepening mid-level trough observed on
    afternoon water vapor imagery, towering cumulus has become
    progressively more agitated from far southeastern Montana into
    northeastern Wyoming. Incipient updrafts along the crest of the Big
    Horns and higher terrain in southeast Montana suggests the airmass
    across the High Plains is likely nearing minimal convective
    inhibition. SPC mesoanalysis indicates between 500-1500 J/kg of
    MLCAPE have developed in a narrow corridor from the Nebraska
    Panhandle northward, owing to steep mid-level lapse rates and
    surface mixing ratios between 8 and 10 g/kg. Weak upslope flow,
    diurnal heating, and background ascent from the approaching
    mid-level wave should further diminish remaining inhibition, and may
    allow for convective development in the next couple of hours. CAM
    guidance remains unreliable in the weak ascent regime, but does hint
    at one or more clusters of storms evolving off the higher terrain
    this evening. The primary severe threats will be damaging outflow
    winds and hail, given moderate buoyancy and steep low/mid-level
    lapse rates.=20

    Across the Black Hills of western South Dakota, cloud debris from
    earlier convection is inhibiting strong surface heating casting
    doubt on storm initiation in this region. Here, deeper surface
    moisture and higher buoyancy may support a locally greater, but more conditional severe threat for wind and hail into this evening. Given
    the narrow corridor of destabilization and the uncertainty on storm coverage/intensity, a weather watch is unlikely, though trends will
    be monitored.

    ..Lyons/Guyer.. 06/19/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!p7l1faDuFhQK5-rnJ1fEDGOAcorHYEQP_pQMVcSIM3fxLxwqju7stH8qikyV-77FUGKX-sZz$=
    for graphic product...

    ATTN...WFO...BIS...LBF...UNR...CYS...BYZ...GGW...

    LAT...LON 42540325 42570417 43430464 44650494 45680493 46490480
    46640474 46820434 46590388 45590312 44680263 43960228
    43370213 42610256 42540325=20



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