FXUS63 KLOT 151158 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 658 AM CDT Wed Apr 15 2026 .KEY MESSAGES... - Additional waves of showers and thunderstorms are expected early this morning through tonight. Some could be severe and produce heavy rainfall leading to flash flooding. - A brief break in the pattern is expected late Thursday into the day on Friday before another storm system arrives Friday evening into early Saturday. - Cooler air arrives into early next week and may bring frost/freeze concerns early Sunday and Monday mornings. && .DISCUSSION... Issued at 343 AM CDT Wed Apr 15 2026 Through Tonight: An elongated axis of elevated showers and thunderstorms continues early this morning from southeast Nebraska through southern Michigan. Some of these storms have taken advantage of a small area of steeper mid-level lapse rates amidst strong effective shear to 50 kt and managed to produce severe hail. Isolated strong to severe storms will remain possible through early this morning. There remains a fair amount of uncertainty with respect to how convective trends unfold the remainder of the day owing to the potential for multiple "waves" of showers and storms. Each model and their respective runs vary on the details, including timing and placement of the different bands of storms and how they interact with each other (outflows, cold pools, etc.). It does appear that after this initial round of stronger storms early this mornings sags farther east and southeast there may be a temporary decrease in the thunderstorm coverage during the rest of the morning hours when lapse rates here locally decrease. Once we get into the afternoon hours the threat of severe weather increases again as lapse rates steepen allowing instability to quickly build over the area (MLCAPE of 2000+ J/kg) amidst ample deep layer shear. The Storm Prediction Center has upgraded the rest of the area to a Level 2 of 5 severe thunderstorm risk which seems appropriate, with the primary hazard being damaging wind gusts with any embedded bowing segments. A locally higher hail threat may materialize with any embedded semi-discrete supercells. Another concern for today is the potential for flash flooding as additional waves of heavy rainfall potentially occur over the same areas. Have extended the Flood Watch in duration and area to account for this. Thursday: A compact shortwave and associated weak surface low/MCV is forecast to move across or near the area during the day on Thursday which will likely be accompanied by additional scattered showers and non-severe thunderstorms. Once that moves off to the east a very brief break in the wet and stormy pattern is expected Thursday night through the day on Friday. Temperatures on Thursday will also end up cooler (albeit still unseasonably warm) with highs in the mid 60s to mid 70s, coolest across far northeast Illinois. Friday - Saturday: Strong southerly warm and moist convection will return into the day on Friday ahead of an approaching cold front. This boundary is expected to progress across the area sometime late Friday into early Saturday morning paired with a line of thunderstorms, some of which could be severe. Suspect that less favorable diurnal timing of any lingering storms into the morning on Saturday may limit the overall severe threat here locally before storms reintensify east of the area into the rest of the day. Stay tuned! Saturday night onward: In the wake of the early Saturday cold front, a much colder airmass (relative to what we have had over the past several days) will settle into the region over the weekend. Overnight low temperatures may drop into the 30s, with some near to sub- freezing temperatures possible across interior northern Illinois. Lighter winds in place Sunday night may allow for frost development outside of Chicago and will be something for those with agricultural interests to monitor over the next few days. The cooler conditions will be rather short-lived with extended guidance favoring a return toward high amplitude ridging across the central CONUS and unseasonably warm temperatures returning to the region by midweek next week. Petr && .AVIATION /12Z TAFS THROUGH 18Z THURSDAY/... Issued at 658 AM CDT Wed Apr 15 2026 Main Concerns: - In the wake of morning SHRA and isolated embedded TS, the potential exists for additional SHRA/TSRA this afternoon and evening, with low confidence in specifics. A fairly coherent area of showers extends back to about the MS River as of this writing. Included VCTS until mid morning for the Chicago metro terminals to account for a few taller convective cores that may produce sporadic lightning. More widespread TS over far western IL should remain safely south of the TAF sites as they lifts northeast through the morning. In the wake of the morning activity, there should be a few to several hour window with isolated to scattered SHRA at most near the terminals. It remains quite unclear where additional SHRA/TSRA will develop this afternoon. More recent guidance has tended to favor south of the terminals this afternoon, with a better chance of TS holding off until this evening. Given the aforementioned lower confidence in specifics, opted to transition back to a broader PROB30 while maintaining the VCTS from previous issuances. Variable/erratic and strong/gusty winds may occur in any on station TS impacts. Wind variability in the wake of the storms would likely follow. Outside of convection, winds will favor a southwest to west direction through Thursday morning, with occasional gusts to ~20 kt. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Flood Watch through late tonight for ILZ003-ILZ004-ILZ005- ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020- ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107- ILZ108. IN...Flood Watch through late tonight for INZ001-INZ002-INZ010- INZ011. LM...None. && $$ Visit us at weather.gov/chicago