• MESO: Mesoscale Discussion 1547

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Aug 17 20:21:46 2021
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    ACUS11 KWNS 172021
    SWOMCD
    SPC MCD 172021=20
    MTZ000-WYZ000-IDZ000-172215-

    Mesoscale Discussion 1547
    NWS Storm Prediction Center Norman OK
    0321 PM CDT Tue Aug 17 2021

    Areas affected...Southern to Southwest Montana

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

    Valid 172021Z - 172215Z

    Probability of Watch Issuance...20 percent

    SUMMARY...Isolated to scattered thunderstorms may be capable of
    severe downburst winds across southwest to southern Montana this
    afternoon and evening. However, this threat will most likely remain
    too isolated to warrant a watch issuance.

    DISCUSSION...A few deeper convective towers with occasional
    lightning have emerged from a growing cumulus cluster over the
    terrain of the ID/MT border over the past hour. This is likely the
    result of increasing instability (MUCAPE values up to 1000 J/kg) and strengthening lift over the region as a surface low slowly deepens
    ahead of an approaching upper-level wave. As forcing for ascent and
    instability continue to increase through the late afternoon
    thunderstorm development will become more likely. Downstream of this
    cluster, temperatures across southern MT have warmed into the upper
    80s ahead of an approaching cold front. Additional boundary-layer heating/mixing will help further steepen low-level lapse rates to
    near 9 C/km, which may already be achieved at a few sites where
    dewpoint depressions near 40 F are noted. Strong flow aloft may
    support some initial storm organization, and the low-level
    thermodynamic profiles will support a severe downburst potential
    with any strong thunderstorm. Scattered storm coverage is possible,
    but the combination of the approaching cold front and patchy cloud
    cover may spatially limit favorable boundary-layer profiles and the
    subsequent severe wind potential. Because of this limitation, a
    watch is not expected at this time.

    ..Moore.. 08/17/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!u8zoX_GVXUxIvc0iLSL1MH0kEARscyHBHAdrZQUFScOigoN5iY7ol7oQ4N8vmGGBbwARV3kA$=
    for graphic product...

    ATTN...WFO...BYZ...GGW...RIW...TFX...PIH...MSO...

    LAT...LON 44891329 45401361 45921327 46921100 47470836 47440716
    47150647 46440652 45440717 45120810 44511151 44421218
    44531281 44891329=20



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