textproduct: Chicago

KEY MESSAGES

- Hot conditions are expected for much of the week; though somewhat cooler near Lake Michigan.

DISCUSSION

Issued at 223 PM CDT Tue Jul 14 2026

An expansive area of high pressure continues to reside over the Midwest and Great Lakes regions which will continue to promote warm and humid conditions. Temperatures will continue to warm into the mid to upper 90s this afternoon with heat indices peaking around the 100 degree mark. While there is a lake breeze oozing inland northeast IL and northwest IN, the inland extent of the lake breeze should be limited given the weaker flow behind it and thus limit lake cooling effects to the immediate shoreline.

Similar conditions are expected for Wednesday with highs once again back into the mid-90s inland with slightly cooler readings (highs in the upper 80s) near the immediate lake shore due to a lake breeze. However, forecast soundings do show slightly better mid-level moisture in place which may lead to the development of some diurnal cumulus clouds. Additionally, some of the wild fire smoke from Canada is progged to round the high pressure and ooze into the area from the east which may further aid to add some haze to the sky and limit some of the incoming solar radiation. While the clouds likely won't have much effect on temperatures on a widespread basis, they may be able to keep temperatures a degree or two cooler in spots that see more clouds and thus result in slight lower heat indices there too. Speaking of heat indices, dew points on Wednesday will once again start off in the lower 70s but should mix down into the upper 60s through the afternoon which will keep peak heat indices around the 100 degree mark once again. Given that our local Heat Advisory criteria is 105 degrees and above, we will be holding off on issuing any heat headlines for tomorrow but will continue to message the heat and encourage everyone to stay hydrated and avoid outdoor activities during the hottest parts of the day.

Heading into Thursday, the high will begin to move east as deeper troughing builds over Ontario and Quebec. At the same time, moisture will be trying to return northward out of the southern CONUS and Gulf. Given that forecast soundings continue to show the deeper moisture still being somewhat limited and the idea that the high should still have majority control, suspect that any showers and storms that try to develop will be very isolated and mainly confined to our far southern and western CWA closer to the northwestward propagating shortwave. With the expectation for more cloud cover on Thursday temperatures will still be warm but a few degrees cooler than Wednesday with highs in the lower 90s. As a result heat indices will also be a bit lower (peaking in the 95-100 degree range) as dew points should once again mix down into the upper 60s to lower 70s which will once again keep us below heat headline criteria. Furthermore, with a signal for a more enhanced lake breeze on Thursday highs near the lake should be more into the mid to upper 80s which will further cap heat indices here into the lower to mid- 90s. This expectation will keep Chicago and Cook County below their three day Extreme Heat Warning Criteria so will forego any such issuance on this shift, but continue to message the heat and need for folks to stay hydrated.

By Friday the high will be far enough east to allow the northwest flow aloft to take control and pivot another shortwave trough through the area. This wave in combination with better moisture and instability should result in a broader coverage of showers and thunderstorms Friday afternoon and evening. Though, with the weaker wind shear the threat for severe weather continues to look low. Additional periods of showers and thunderstorms are expected through the weekend and into the early part of next week as shortwaves continue to traverse the pattern and dive through the region. Temperatures through the end of the week are expected to remain near to above average with daily highs in the upper 80s and 90s.

Yack

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/

Issued at 1250 PM CDT Tue Jul 14 2026

- Light east wind shifts with the lake breeze at ORD/MDW each afternoon

Main concern through the period is the timing of weak lake breezes at MDW/ORD this afternoon and again Wednesday afternoon. Have slowed the arrival of the lake breeze this afternoon in the TAFs by an hour, 19Z MDW and 20Z ORD, though given the very weak surface flow will have to monitor observational trends for any surges or stalling of the boundary over the next few hours. Speeds are expected to remain light but can't rule out a brief period of speeds around 7-9 kt with the initial wind shift. Winds then return to a west direction later this evening through early Wednesday afternoon before another lake breeze turns winds east at ORD/MDW/GYY. Farther inland (DPA/RFD) expect light west to at times variable winds through the period.

VFR conditions are currently forecast with some passing high cirrus and a thin smoke layer aloft possible at times. Can't rule out shallow ground fog/BR out toward RFD early Wednesday morning but confidence is not high enough to include with this update. Surface visibility reductions due to smoke will also need to be monitored toward the end of or just beyond the current 30-hr TAF period.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...Air Quality Alert until midnight CDT Wednesday night for ILZ005-ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

IN...Air Quality Alert until midnight CDT Wednesday night for INZ001-INZ002-INZ010-INZ011.

Air Quality Alert from midnight tonight to 1 AM EDT Thursday for INZ019.

LM...None.