SPC MD 309

MD 0309 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR PARTS OF NORTHERN AND CENTRAL ILLINOIS...NORTHERN INDIANA Mesoscale Discussion 0309 NWS Storm Prediction Center Norman OK 0244 PM CDT Tue Mar 31 2026 Areas affected...parts of northern and central Illinois...northern Indiana Concerning...Severe potential...Watch possible Valid 311944Z - 312215Z Probability of Watch Issuance...40 percent SUMMARY...Isolated to widely scattered strong thunderstorm development, including a couple supercells, appears possible late this afternoon. It remains unclear if a new severe weather watch will be needed, but trends are being monitored for this possibility. DISCUSSION...In the wake of early day convection, substantive pre-cold frontal boundary-layer destabilization appears ongoing in a corridor across northern/central Illinois through northern Indiana. This is occurring beneath 40-50 kt westerly flow around 500 mb, near the southern fringe of the stronger westerlies, but in the wake of one low-amplitude short wave migrating toward the lower Great Lakes and generally well south of broad mid-level troughing overspreading the Upper Midwest and adjacent upper Great Lakes region. Models indicate at least subtly building mid-level heights across the region into this evening. However, low-level warm advection may be contributing to ongoing renewed thunderstorm development southeast of Davenport IA toward southern portions of the Greater Chicago area. And, at least some convection allowing guidance suggests that a subtle linger mid-level perturbation, now progressing west-northwest through north of the Greater St. Louis area, may support additional storm development during the next few hours. While it remains unclear how widespread or organized convection may become, the environment appears at least conditionally supportive of supercells with potential to produce large hail, locally damaging wind gusts, and perhaps a brief tornado. ..Kerr/Hart.. 03/31/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...IWX...IND...LOT...ILX...LSX...DVN... LAT...LON 40249098 41189006 41518512 40618530 39258855 38889022 40249098 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN Read more