• MESO: Mesoscale Discussion 1155

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Jul 5 18:34:28 2021
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    ACUS11 KWNS 051834
    SPC MCD 051834=20

    Mesoscale Discussion 1155
    NWS Storm Prediction Center Norman OK
    0134 PM CDT Mon Jul 05 2021

    Areas affected...portions of Montana Wyoming and South Dakota

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

    Valid 051834Z - 052030Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Isolated strong/severe storms will likely develop in
    response to warm advection near a frontal zone across the High
    Plains early this afternoon. Isolated instances of hail and damaging
    winds will be possible. A better organized severe threat will likely
    evolve across western portions of South Dakota this evening. A
    weather watch is possible but uncertain in the short term.

    DISCUSSION...Early afternoon water vapor imagery showed a weak vort
    max traversing the central Rockies across portions of western
    Wyoming. Ahead of this feature, several other weak disturbances
    evident in lower-level imagery were crossing the Dakotas and High
    Plains, where remnant morning convection and additional
    boundary-layer cumulus have become more numerous in the past half
    hour. Likely related to weak warm advection/forcing for ascent along
    a diffuse frontal zone, this convection and additional storms should
    track southeastward across South Dakota along the instability axis
    (1500-2500 J/kg MUCAPE). On the fringes of stronger mid-level flow
    aloft, vertical shear less than 30 kts should favor modestly
    organized multicellar clusters. Likely rooted above the surface
    given considerable MLCINH remaining on SPC mesoanalysis, these
    storms/clusters will present mainly a risk for large hail initially,
    before gradually becoming more surface based this afternoon/evening.

    To the west northwest across portions of eastern Wyoming and the
    Black Hills, boundary-layer cumulus was noted developing in a weak
    upslope flow regime. As lift from the approaching trough and
    orographic forcing continue to reduce inhibition, additional storms
    should develop later this afternoon. With 1000-2000 J/kg of MLCAPE
    and enhanced vertical shear around 30-35 kts ahead of the wave,
    organized multicell clusters and perhaps a few supercells appear
    likely to evolve. Damaging wind gusts and hail will be likely with
    the strongest storms as they track to the east southeast into this
    evening. Some upscale growth into one or more small MCS with a risk
    of damaging winds into the overnight hours also appears probable.

    Uncertainty remains high on the threat through the short term with
    trends suggesting the potential for organized severe weather
    remaining quite limited. The need for a weather watch appears more
    likely later in the day for more robust convection developing to the
    west. As such, convective trends will be monitored or a possible
    weather watch this afternoon, though the need for a watch in the
    short term remains uncertain.

    ..Lyons/Guyer.. 07/05/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!vnqvwdHpu11UuvhgwKlLkG129QXnybggeAgtaqsgLrQ5A0DKKDS8ETHC83HiIWx7IVG1uq3m$=
    for graphic product...


    LAT...LON 45780418 45940374 45920304 45360141 44960038 44559938
    44019834 43749814 43349814 43079844 43039914 43029966
    42990029 42960140 43060371 43100429 43630466 44630464
    45260450 45780418=20

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