Mesoscale Discussion 1941
Issued: · Valid: –
Summary
Strong to severe thunderstorms capable of producing large hail and damaging wind gusts may develop across eastern Iowa, northern Illinois, and northwest Indiana between 02:00 and 05:00 UTC. These storms could become severe, with potential for very large hail and wind gusts up to 70 mph.
Product Text
000 ACUS11 KWNS 120104 SWOMCD SPC MCD 120104 INZ000-ILZ000-WIZ000-IAZ000-120330- Mesoscale Discussion 1941 NWS Storm Prediction Center Norman OK 0804 PM CDT Tue Aug 11 2026 Areas affected...Eastern Iowa into northern Illinois and far northwest Indiana Concerning...Severe potential...Watch possible Valid 120104Z - 120330Z Probability of Watch Issuance...60 percent SUMMARY...Strong to severe thunderstorms may materialize between 02-05 UTC across northern Illinois into northern Indiana. These storms will pose a risk of large to very large hail and severe gusts. Trends will be monitored, and watch issuance may be needed. DISCUSSION...The northwestern edge of the cold pool associated with the earlier passage of an MCS is becoming increasingly diffuse across northern IL based on recently surface observations with temperature warming back into the upper 70s and briefly into the 80s before the onset of nocturnal cooling. Aloft, westerly 700-500 mb flow has advected steep lapse rates eastward back into the region, which were well sampled by the recent DVN and ILN 00 UTC RAOBs. As a result, the thermodynamic environment is steadily destabilizing and becoming increasingly supportive of intense convection. (These soundings also sampled extreme buoyancy between 4000-5000 J/kg MLCAPE and weak inhibition around -50 J/kg.) Over the past few hours, a subtle disturbance has been tracked across IA, evident by weak mid-level ascent. This feature has been supporting weak attempts at convection across southern MN and western WI, and will likely promote additional attempts within the destabilizing air mass across far eastern IA into northern IL later this evening. Latest guidance suggests that convective initiation is likely between 02-05 UTC, and will likely be focused along and north of the residual outflow boundary. Initially discrete to semi-discrete cells may mature into supercells before storm interactions within the zone of ascent promote clustering and upscale growth. Large to very large hail will be possible given the ample buoyancy and around 40 knots of effective shear if initially discrete modes can be adequately sustained. Strong to severe winds also appear possible given the shallow nature of the residual cold pool across northern IL. It remains unclear exactly how long discrete storm modes will persist and how far downstream into IN convection will develop. Regardless, trends will be monitored, and watch issuance is probable given the favorable convective environment. ..Moore/Mosier.. 08/12/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...IWX...IND...LOT...ILX...MKX...DVN...ARX... LAT...LON 40168790 41669142 41919167 42299174 42649163 42819136 42919083 42859053 41848731 41518698 41158685 40798685 40478695 40258713 40148731 40088754 40168790 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN