Mesoscale Discussion 2075 NWS Storm Prediction Center Norman OK 0613 PM CDT Fri Aug 21 2026 Areas affected...Parts of northern IL...far southern WI...and far east-central IA Concerning...Severe Thunderstorm Watch 610... Valid 212313Z - 220115Z The severe weather threat for Severe Thunderstorm Watch 610 continues. SUMMARY...An increase in thunderstorm intensity is possible during the next few hours. Damaging winds and large hail are still the main concerns, though a tornado or two cannot be ruled out. DISCUSSION...Over the last 30 minutes or so, a couple thunderstorms have increased in intensity across northern IL and far east-central IA, as a subtle frontal wave low approaches the area from the west. In particular, one evolving supercell is interacting with a remnant outflow boundary in parts of Lee, La Salle, and Bureau Counties IL. Given an estimated south-southeastward storm motion (per nearby VWP), this storm could maintain residence time along the immediate warm side of the boundary and pose an increased risk of damaging winds, large hail, and possibly a tornado in the near term. Farther west, additional thunderstorms are intensifying in a zone of enhanced low-level convergence closer to the frontal wave low in northwest IL and far east-central IA. Warm/moist inflow for these storms and 30-40 kt of 0-6 km shear (per nearby VWP data) oriented perpendicular to the zone of low-level convergence should promote an increase in thunderstorm organization/intensity during the next few hours. Damaging winds and large hail continue to be the main concerns, though a tornado or two will also be possible, given some increase in low-level shear ahead of the frontal wave during the next few hours. ..Weinman.. 08/21/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LOT...ILX...MKX...DVN... LAT...LON 40938944 41419018 41809030 42219028 42479008 42688933 42618875 42418849 41998835 41078851 40898887 40938944 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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