textproduct: Chicago

KEY MESSAGES

- The potential for showers and thunderstorms returns on Wednesday along a cold front, some could be strong to severe.

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 in 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 /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1241 PM CDT Mon Aug 24 2026

Key Messages:

- A lake breeze will result in an easterly wind shift at ORD and MDW this afternoon.

- There is some potential for visibility reductions from ground fog tonight into tomorrow morning at RFD, DPA, and GYY, but confidence in this occurring is low.

A lake breeze stalled over the city of Chicago at press time will eventually make a push inland this afternoon and result in an easterly wind shift at ORD and MDW. An easterly wind shift may also occur at DPA towards sunset before the lake breeze washes out this evening. Another lake breeze will develop tomorrow and may result in squirrelly wind directions at GYY for some time, but will likely remain east of ORD and MDW, where southwesterly winds are likely to prevail tomorrow.

Similar to this morning, there is also some potential for visibility reductions from ground fog to occur at RFD, DPA, and GYY tonight into tomorrow morning. The better signal for impactful fog in forecast guidance is to the south of these terminals, so have maintained prevailing VFR conditions in their respective TAFs for now, but certainly couldn't rule out eventually needing to introduce a mention of lower visibility (most likely in the 4-6 SM range) into these TAFs at some point.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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