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  • MESO: Mesoscale Discussion 1746

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Jul 21 20:00:14 2025
    ACUS11 KWNS 212000
    SWOMCD
    SPC MCD 211959=20
    SDZ000-NDZ000-MTZ000-WYZ000-212200-

    Mesoscale Discussion 1746
    NWS Storm Prediction Center Norman OK
    0259 PM CDT Mon Jul 21 2025

    Areas affected...portions of central and eastern MT into western
    ND/SD and northeast WY

    Concerning...Severe potential...Watch likely=20

    Valid 211959Z - 212200Z

    Probability of Watch Issuance...80 percent

    SUMMARY...Severe thunderstorm potential will increase over the next
    1-3 hours. Potential for large hail 2.5-3.0 inches in diameter,
    damaging gusts to 80 mph, and possibly a tornado will be possible
    into the evening hours. A severe thunderstorm watch is likely for
    parts of the discussion area by 22z.

    DISCUSSION...Isolated thunderstorms and increasing cumulus are noted
    near the higher terrain of northern WY/southern MT. This activity is
    developing within drier air and strong differential heating over
    higher terrain and as increasing large-scale ascent begins to
    impinge on the area from the west. With time, additional convection
    is expected to spread northeast into an axis of great boundary-layer
    moisture in the upper 50s to low 60s F from central MT into the
    western Dakotas.=20

    Favorable vertical shear amid a roughly west to east oriented tongue
    of modest to strong instability will support initial cells capable
    of large hail. Steepened low-level lapse rates and at least some
    modest dry air noted in forecast soundings centered around 700 mb
    suggests strong winds also will be possible. This may especially
    occur if any clusters/bows develop as a low-level jet increases
    during the evening, and with eastward into the western Dakotas. As
    storms interact with the moist axis across southeast MT, some
    potential will exist for a tornado or two if capping is sufficiently
    eroded and where backed low-level winds will result in locally
    enhanced 0-1 km SRH.

    Initial severe thunderstorm watch issuance is expected by 22z,
    though eastern extent of watch issuance is a bit uncertain and may
    or may not extend into the western Dakotas with this watch issuance.

    ..Leitman/Smith.. 07/21/2025

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!_ePNP7xULzwRvwjYzaEC40H7Iz6PZpWXH9ORGHT9249Wesnhj2fgSzhnB9wMKM1vKW0md2q3n= FAGDJLitapt4lt-6RI$ for graphic product...

    ATTN...WFO...BIS...UNR...BYZ...GGW...TFX...

    LAT...LON 44260422 44220359 44340317 44820295 45760286 46920302
    47720348 48090542 47840790 47101010 46681056 46231074
    45551031 45170739 44880570 44260422=20

    MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
    MOST PROBABLE PEAK WIND GUST...65-80 MPH
    MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN


    =3D =3D =3D
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