Mesoscale Discussion 1237 NWS Storm Prediction Center Norman OK 0653 PM CDT Sun Jun 21 2026 Areas affected...southern Illinois into southern and central Indiana Concerning...Tornado Watch 363...365... Valid 212353Z - 220130Z The severe weather threat for Tornado Watch 363, 365 continues. SUMMARY...The tornado threat continues across Tornado Watches #363 and #365. DISCUSSION...Supercells with a history of producing tornadoes are ongoing across Tornado Watches #363 and #365 this evening. The overall environment remains very favorable for thunderstorm rotation, with effective-layer shear on the order of 40-50 knots and 0-3 kilometer SRH ranging from 400 m2/s2 from the Evansville, IN, VAD to over 600 m2/s2 from the Indianapolis, IN, VAD. Likely contributing to this enhanced low-level helicity is a strong easterly component to the low-level wind field in response to an MCV tracking northeast into central Indiana. As this MCV moves northeast toward Indianapolis, increasing low-level theta-e to the south and east of the MCV should be sufficient to offset the loss of diurnal heating to maintain sufficient instability into the evening hours, particularly across the watch area. Thus, the threat for thunderstorms will continue. The threat for tornadoes will exist as long as ongoing thunderstorms can remain sufficiently rooted in the boundary layer to ingest these helicity-rich low-level air parcels. As storms move east of I65, low-level theta-e quickly drops off and storms should become increasingly elevated. As this occurs, the overall tornado threat should lessen and a transition to strong, damaging winds may occur before thunderstorms weaken. ..Marsh.. 06/21/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ILN...LMK...IND...PAH...ILX...LSX... LAT...LON 38599018 39518828 39848672 39738536 38728522 38098731 37678889 37799007 38599018 MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH MOST PROBABLE PEAK WIND GUST...65-80 MPH MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
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