ZCZC SPCSWOMCD ALL ACUS11 KWNS 202055 SPC MCD 202055 WIZ000-MIZ000-IAZ000-MNZ000-202230- Mesoscale Discussion 1770 NWS Storm Prediction Center Norman OK 0355 PM CDT Mon Sep 20 2021 Areas affected...portions of central into eastern Iowa...far southeast Minnesota...western into northern Wisconsin Concerning...Severe Thunderstorm Watch 507... Valid 202055Z - 202230Z The severe weather threat for Severe Thunderstorm Watch 507 continues. SUMMARY...The severe threat continues with Severe Thunderstorm Watch 507, and should persist through the afternoon. Damaging gusts and occasional large hail are expected to remain the primary threats, though a brief tornado cannot be completely ruled out. A new WW may be needed to the northeast of Severe Thunderstorm Watch 507. DISCUSSION...Temperatures have reached or exceeded 80F across much of the warm sector ahead of the ongoing line of storms, south of a warm front draped across northern WI, contributing up to 1500 J/kg MLCAPE in spots. Storms along/ahead of the eastward advancing cold front have obtained predominantly linear structures, posing a threat for mainly damaging gusts, though a couple instances of marginally severe hail remain possible, especially across northern portions of Severe Thunderstorm Watch 507 given 45+ kts of effective bulk shear in place. While the tornado threat is expected to remain limited overall, over 200 m2/s2 of effective SRH has been noted in proximity to the warm front by the 20Z mesoanalysis, with the 2024Z ARX VWP showing well over 200 m2/s2 SRH within the 0-1 km layer alone. Despite the linear storm mode, any segment which can become more northwest-southeast aligned (oriented relatively more normal to the 45+ kt effective bulk shear vector) would support some potential for a brief tornado given adequate buoyancy. ..Squitieri/Hart.. 09/20/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MQT...GRB...DVN...DLH...ARX...MPX...DMX... LAT...LON 40629466 42649403 44469346 45559311 46119259 46489176 46509074 46318999 45898955 44719025 42379077 40859166 40619188 40629466 NNNN