textproduct: Chicago

KEY MESSAGES

- The next chance of showers and thunderstorms is with a cold front moving across the area midweek.

DISCUSSION

Issued at 212 AM CDT Mon Aug 24 2026

High pressure continues to settle into the mid-Mississippi Valley and will remain in place through Tuesday. As a result, dry conditions with generally comfortable humidity are expected to start off the work week. Temperatures today will once again be on the seasonably cool side with highs only topping out in the upper 70s to around 80 this afternoon. A lake breeze is expected to develop and move inland this afternoon and evening which will result in cooling temperatures along the lakeshore, though with lake temperatures in the lower 70s the temperature drop shouldn't be overly impressive. Overnight lows tonight won't be as chilly as they will be this morning, but will dip into the mid-50s inland with upper 50s near the lake. As winds turn more south-southwesterly on Tuesday, warmer air should begin to advect into the area and result with more seasonable highs in the lower 80s. Rain chances are still forecast to increase as we head into the middle of the week as the shortwave trough over the Mountain West pivots into the Great Lakes. A cold front is expected to accompany the shortwave as it moves through the region which should serve as the impetus for showers and thunderstorms. Similar to last night, guidance continues to show some showers/storms developing along the front in the Upper Midwest on Tuesday and drifting towards northern IL Tuesday night. Though, with moisture return continuing to look more limited locally and the unfavorable diurnal time, these showers/storms should be in a decaying state as they approach IL (if they make it at) so the greatest coverage of any rain Tuesday night should be near the IL-WI line. The front is expected to continue moving across northern IL and northwest IN on Wednesday which should allow for the redevelopment of showers and thunderstorms Wednesday afternoon and evening as diurnal destabilization occurs. Despite the decent MLCAPE values noted in forecast soundings, shower and storm coverage continues to look spotty likely due to weaker frontal convergence and the core of the shortwave currently forecast to be centered over MI. So while this may mean some areas get little rain, our official forecast will continue to advertise broad 30 to locally 50% chances for showers and storms on Wednesday. Regardless of storm coverage, deep layer shear values of 25-35 kts are still expected in the area which may support a few storms becoming strong to locally severe Wednesday afternoon and evening. The Storm Prediction Center has added a marginal (level 1 of 5) risk to our area for Wednesday because of this potential.

The cold front should exit the area late Wednesday night into Thursday morning which looks to allow another surface high to build into the area. However, with some subtle frontal timing differences noted in ensemble guidance the exact time the front exits remains uncertain. Nevertheless, the building high pressure behind the front will result in a period of dry weather to close out the work week with otherwise seasonable temperatures expected. The signal remains for a shift towards a more active upper-level pattern as we head towards the beginning of next week which looks to mean more shower and thunderstorm chances so enjoy the nice weather while we have it.

Yack

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1248 AM CDT Mon Aug 24 2026

Key aviation forecast messages:

- Lake breeze may turn winds east this afternoon at ORD/MDW

Winds will remain light and variable through daybreak, potentially leaning more consistently westerly at the Chicago terminals due to a weak land breeze. Winds then settle into a prevailing NW to NNW after daybreak around 5-10 kt. A lake breeze is forecast to drift inland during the afternoon. While confidence in the timing that it reaches ORD/MDW remains on the lower side, did move up the wind shift by an hour at MDW to 20Z based on hi-res guidance trending a bit earlier there (maintained 22Z at ORD for now).

VFR conditions are forecast through the period with varying coverage of diurnal cumulus around 5000 ft and occasional higher clouds. Can't fully rule out shallow fog (MIFG) developing outside of Chicago early this morning but the potential is too low to include a formal TAF mention.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.