FXUS63 KLOT 150843 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 343 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 could 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 favoring areas near and north of I-80. 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 with a locally higher hail threat across northern/northwest Illinois, including the Rockford area where embedded supercells or semi-discrete storm mode can't be ruled out. Another concern for today is the potential for flash flooding as additional waves of heavy rainfall potentially occur over the same areas. Will likely end up needing to extend the current 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 /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1210 AM CDT Wed Apr 15 2026 Aviation forecast concerns for the 06Z TAFs: - Periods of TSRA, particularly remainder of overnight, and again late Wednesday afternoon/evening. Brief IFR/MVFR possible in precipitation. Scattered SHRA possible at other times. - Winds likely convectively disturbed with somewhat variable directions for the next several hours, otherwise mainly southwest to south winds (breezy at times with gusts 20-25 kts). Late evening surface analysis depicts an area of low pressure over north-central KS, with a quasi-stationary frontal boundary extending northeast across IA into southern WI. A thunderstorm complex which moved across northern IL late Tuesday evening was moving east across lower MI, though storms continue to redevelop back across northwest IN/northeast IL along and northeast of a west-east oriented outflow boundary trailing the aforementioned complex. Additional thunderstorms have developed along the stationary front roughly along a a KOMA-KDSM-KCID line. Expectation is that scattered TS will continue to redevelop across the Chicago terminals as the low-level jet ascends atop the west-east outflow boundary, at least for another 2-3 hours or so. High-res guidance (RRFS/HREF) indicates IA TSRA will spread into parts of northern IL after 09-10Z, potentially lingering through daybreak or slightly later before weakening and moving east of the area. Terminals will remain within a region of broad southwest warm/moist advection however, which could result in isolated/scattered SHRA just about any time Wednesday. Can't rule out some isolated TS during the day, though the next best window for greater TSRA coverage appears to be late Wednesday afternoon into Wednesday evening/night. Surface winds have become convectively disturbed across northern IL at this time in the wake of the departing complex. While winds should eventually settle back to a south-southwest, current winds do have some variability in direction north of the aforementioned outflow boundary. Once winds do shift back to the south-southwest, breezy conditions are likely with gusts 20-25 kts at times. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Flood Watch until 6 AM CDT early this morning for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ011-ILZ012-ILZ013-ILZ020- ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108. IN...Flood Watch until 6 AM CDT early this morning for INZ001. LM...None. && $$ Visit us at weather.gov/chicago