Severe Storm Outlook Narrative (AC)
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Issued by NWS
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922 ACUS11 KWNS 221757 SWOMCD SPC MCD 221756 ILZ000-WIZ000-IAZ000-222000- Mesoscale Discussion 1372 NWS Storm Prediction Center Norman OK 1256 PM CDT Sat Jun 22 2024 Areas affected...Portions of northeastern IA...northern IL...and southern WI Concerning...Severe potential...Watch likely Valid 221756Z - 222000Z Probability of Watch Issuance...95 percent SUMMARY...Severe storms capable of producing damaging winds, a couple tornadoes, and isolated large hail are expected this afternoon into the evening. A watch is likely in the next hour or two. DISCUSSION...Latest visible satellite imagery indicates filtered diurnal heating/destabilization of a very moist boundary layer (middle 70s dewpoints) along/south of an east/west-oriented stationary boundary extending across portions of northern IA into southern WI. Over the next couple hours, a weak frontal wave currently near far northwest IA will track eastward along the boundary, promoting scattered thunderstorm development -- aided by the aforementioned destabilization and modest midlevel height falls ahead of a midlevel trough. Around 50 kt of midlevel westerly flow atop a 30-40-kt southwesterly low-level jet (per regional VWP) will promote organized surface-based storms (including a few supercells) near the boundary. Easterly storm motions and deep-layer shear parallel to the boundary may favor congealing cold pools and localized upscale growth, though the favorable shear profile (large clockwise-curved low-level hodographs) should encourage a few sustained semi-discrete supercells. Damaging winds up to 70 mph, a couple tornadoes, and isolated large hail are all possible with this activity. Current thinking is that severe storms will develop/mature in the 19-20Z time frame and persist into the evening hours. A watch is likely for parts of the area in the next hour or two. ..Weinman/Hart.. 06/22/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LOT...MKX...DVN...ARX...DMX... LAT...LON 41729328 41889371 42309395 42769393 43079356 43249277 43389085 43338912 43088858 42328852 41908884 41708959 41649094 41679239 41729328