• MESO: Mesoscale Discussion 1184

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Jul 7 20:12:11 2021
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    ACUS11 KWNS 072012
    SWOMCD
    SPC MCD 072011=20
    NEZ000-SDZ000-WYZ000-072215-

    Mesoscale Discussion 1184
    NWS Storm Prediction Center Norman OK
    0311 PM CDT Wed Jul 07 2021

    Areas affected...eastern Wyoming southwestern South Dakota and
    portions of the Nebraska Panhandle.

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

    Valid 072011Z - 072215Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Model guidance and observational trends continue to
    suggest that isolated storm development may take place this
    afternoon and evening. A supercell or two will be capable of mainly
    a hail and damaging wind threat this evening. A tornado or two may
    also be possible. A weather watch is possible, but uncertain given
    the low expected storm coverage.

    DISCUSSION...Within a weak upslope flow regime north of a warm
    front, towering cumulus has been observed percolating along western
    portions of the Pine Ridge and southern Black Hills across eastern
    Wyoming and southwestern South Dakota. Under the influence of a weak
    shortwave trough around the periphery of a mid-level ridge,
    background ascent and surface heating should continue to weaken
    inhibition enough for convective initiation by mid to late
    afternoon. Surface temperatures in the 80s and dewpoints in the mid
    50s to low 60s F along with steep lapse rates around 8 C/km will
    contribute to moderate buoyancy with 1500-2000 J/kg of MLCAPE
    developing by late this afternoon. Model soundings and VWPS show
    enhanced mid-level flow associated with the shortwave trough
    overspreading much of the eastern Wyoming supporting 30-40 kts of
    effective shear. Relatively long but straight hodographs will
    support supercells as the primary storm mode. Given favorable
    kinematic and thermodynamic profiles, these storms may pose a risk
    for large hail (some 2+ inches) and damaging wind gusts through this evening.=20

    Thunderstorm initiation along the western Pine Ridge escarpment in
    Converse, Niobrara, and Campbell Counties, Wyoming and across the
    southern Black Hills appears probable by 21-22z. Within this
    corridor and the southern Black Hills Convergence Zone, locally
    backed winds may also support a risk for a brief tornado with more well-developed supercells as they track southeastward. The threat
    for tornadoes does appear low however, given high-based storms and
    weak low-level shear.=20

    Severe weather appears increasingly likely across the area though
    uncertainty on storm coverage remains high. Trends will be monitored
    for a possible weather watch, but it remains unclear if one will be
    needed.

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

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!spif-AkV64USIukiTsJkWM04m5nnQqMpbkIfZjpEv7LhbwgYsbJRCvR_jhYqSUdNkE5FZypH$=
    for graphic product...

    ATTN...WFO...LBF...UNR...CYS...

    LAT...LON 41550347 42050422 42640474 43460527 43890537 44340489
    44540422 44130355 43410303 42890272 42210250 41600277
    41550347=20



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