FXUS63 KLOT 150510 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1210 AM CDT Wed Apr 15 2026 .KEY MESSAGES... - Late spring to summer-like temperatures continue through Friday with highs in the 70s and 80s and lows in the 60s. - Threat for additional isolated to scattered severe weather overnight and on Wednesday PM, along with a heavy rain and associated flash flooding threat from repeated rounds of thunderstorms overnight into Wednesday. - A brief break in the pattern is expected late Thursday into or through the day on Friday before another storm system arrives in the Friday evening to Saturday timeframe. - In the wake of the Saturday cold front, a brief, potentially sharp, shot of much cooler air could bring frost/freeze concerns into next Sunday and Monday. && .DISCUSSION... Issued at 312 PM CDT Tue Apr 14 2026 Through Wednesday night... The primary weather focus in the near term continues to revolve around the continued threat for a significant severe weather event this evening. This includes the threat of tornadoes, instances of very large hail (2"+ diameter) and damaging winds in excess of 70 mph. The threat of flash flooding is also of increasing concern tonight into Wednesday, due to repeated rounds of very heavy rain producing storms. A recent surface analysis indicates that the stalled west-to- east oriented frontal boundary continues to reside north of the area this afternoon, generally from northeastern IA eastward across southern WI. Meanwhile, the outflow boundary from this mornings convection has largely washed out, with a notable airmass recovery across northeastern IL, noted by temperatures rebounding into the low 80s amidst surface dewpoints in the mid 60s. Interestingly, while this afternoon's airmass recovery beneath a corridor of very steep mid-level lapse rates has resulted in moderate to strong MLCAPE values in excess of 3,000 j/kg, a notable capping EML inversion remains in place. This is apparent on the 18Z DVN RAOB, with a sharp EML inversion noted around 800 mb. While this cap is currently curtailing convective development, the sampled thermodynamic and kinematic environment is quite volatile and will be supportive of significant severe weather as we head through the evening. While some isolated to widely scattered supercells capable of producing large hail will be possible this afternoon as a subtle impulse continues to slide eastward across central and eastern IL into northwestern IN, the primary severe thunderstorm threat continues to be this evening, particularly across northern IL and southern Wisconsin. Initial severe storm development is expected near the stalled frontal boundary in northeastern IA within the next hour or two. In fact, current satellite and radar imagery indicate several convective attempts already underway in this area. As development occurs, storm modes will initially favor supercells, though a eventual upscale growth is anticipated through the evening. Very steep mid-level lapse rates and long straight hodographs will favor instances of very large destructive hail with these initial supercells. However, strengthening low- level flow and the associated enlarging low- level hodographs into early this evening will will support a notable tornado threat for a few hours this evening (6-9 pm). This tornado threat is expected to be the highest across far northern IL into southern WI (generally along and north of I-88). Upscale growth into a severe wind producing MCS, with potential embedded QLCS tornadoes is then likely to occur through the evening as this activity progresses eastward through southern WI and far northern IL. Accordingly, the main severe threats look to transition to damaging wind gusts in excess of 70 mph and isolated tornadoes later this evening. Increasingly confidence has prompted the recent issuance of a tornado watch for most of northern IL through this evening. While the severe threat should largely wane by midnight tonight, the threat for training showers and thunderstorms may continue across parts of northern IL into the overnight hours. A veering low-level jet overnight may set up favorable conditions for training and backbuilding storms as the flow offsets the easterly movement. This adds concern for flash flooding, particularly given that this activity could train over the urban areas of Chicago. At this time we have opted to hold off on a flash flood watch, though as trends become more clear this evening one may be needed. We did highlight the threat for possible flooding concerns in a Hydro outlook (ESF), but again, messaging may need to be ramped up to a Watch this evening. Additional waves of showers and thunderstorms are expected on Wednesday. The amount of cloud cover and periods of rain does make it unclear as to the extent and coverage of severe storms due to questions of diurnal destabilization. Nevertheless, a level 1 to 2 out of 5 severe weather threat continues on Wednesday afternoon and evening. Regardless of the overall severe threat, flooding and flash flooding will continue to be of concern Wednesday into Wednesday night, owing to the repeated instances of very heavy rainfall. Accordingly, a future flood watch may be needed for the tonight through Wednesday time period. Thursday onward... A short period of drier weather is expected late Thursday into Friday morning following the eastward departure of the mid- level impulse ejecting out of the Desert Southwest. However, yet another storm system and associated cold front is favored to shift across the central CONUS Friday night into Saturday morning. Locally, another threat of strong to severe thunderstorms will exist in advance of cold front, which should move across our area sometime Saturday morning. In the wake of this cold front, a period of much cooler weather will move in across the area Sunday into Monday. The magnitude of this colder airmass may result in freezing overnight low temperatures and afternoon highs only in the low 50s for Sunday. KJB && .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 Wednesday for ILZ003-ILZ004-ILZ005- ILZ006-ILZ008-ILZ011-ILZ012-ILZ013-ILZ020-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108. IN...Flood Watch until 6 AM CDT Wednesday for INZ001. LM...None. && $$ Visit us at weather.gov/chicago