Mesoscale Discussion 2321 NWS Storm Prediction Center Norman OK 1152 PM CDT Sun Sep 20 2026 Areas affected...portions of eastern Colorado and extreme western Kansas Concerning...Severe Thunderstorm Watch 674... Valid 210452Z - 210615Z The severe weather threat for Severe Thunderstorm Watch 674 continues. SUMMARY...Strong-to-severe thunderstorms will continue this evening into the early morning hours. Large hail and strong damaging thunderstorm winds will be possible. DISCUSSION...Scattered strong-to-severe thunderstorms, including severe supercells, are ongoing this evening across eastern Colorado. These supercells are capable of producing large-to-very-large hail, with MRMS MESH episodically exceeding 2 inches across many of these storms. Additionally, the supercell across Crowley County, Colorado, is exhibiting signs of strong, perhaps damaging, convective outflow winds. Overall, these storms will continue to move southeast, with the storms having the strongest mesocyclones favoring a more southerly direction. The background environment remains conducive for severe thunderstorms. MUCAPE is in excess of 1000 J/kg with effective layer shear exceeding 40 knots is more than sufficient to sustain ongoing supercells and an attendant large-hail threat into the early morning hours. With time, however, increasing precipitation coverage should weaken the overall instability and lead to a decrease in the overall severe threat. Until that happens, large hail and damaging thunderstorm winds will continue as individual storms move southeast across the area. ..Marsh.. 09/21/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DDC...GLD...PUB...BOU... LAT...LON 37840462 38010503 38840504 39840504 40130505 40420458 40170364 39840281 39440213 39060183 38470171 37970165 37590191 37620347 37840462 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...65-80 MPH MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN
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