textproduct: Chicago

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 /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1245 PM CDT Wed Apr 15 2026

Key Aviation Messages for the current TAF period:

- Lingering VFR showers through this afternoon with gusty southwest winds

- Two rounds of storms with better chances at/near terminals late this afternoon through midnight. Some of these storms could be strong to severe.

- Weaker showers fester through tomorrow morning.

- Wind shift to the northeast tomorrow afternoon

A surface low, currently analyzed just north of Kansas City, Missouri, will move east-northeast through today and the overnight. This low will be the driving force behind the shower and storm threat tonight. In the meantime, weak rain showers persist this afternoon out ahead of it. Winds will remain out of the southwest through most of the TAF window, with persistent gusts 20 to 25 knots, not diminishing until after midnight.

As the low moves closer, it will push a warm front northward through Illinois for the first wave of showers and thunderstorms this evening. There could be a dry slot for a couple hours, but then as the low passes north of the area, it will drag a cold front across northern Illinois for a second round of showers and thunderstorms across the airspace. Some of these storms could become strong to even severe, producing hail and erratic, strong wind gusts.

As the front moves east, showers could fester through the morning. There is lower confidence in ceiling trends due to model disagreement, but erred more cynical behind the low and forecasted widespread MVFR conditions across the region through the morning. Winds will become more westerly in the morning, but as the low continues its journey east of the area, models are suggesting a weak front will be sent southward across Lake Michigan and switch winds over to the northeast tomorrow afternoon.

DK

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.