textproduct: Chicago

KEY MESSAGES

- Hot conditions will continue through the week with high temperatures generally in the upper 80s to 90s and overnight lows in the 70s.

- A period of reduced visibility in smoke may occur on Thursday generally along and northeast of Interstate 90.

UPDATE

Issued at 839 PM CDT Tue Jul 14 2026

It is another warm and beautiful mid-summer night with clear skies, temperatures in the mid 80s, and a light southwesterly breeze. Humidity levels are a hair higher compared to last evening thanks to evapotranspiration from area agricultural fields within the relatively stagnant airmass. As temperatures cool toward the low to mid 70s overnight, can easily envision pockets of fog developing particularly in open areas much like what happened last night.

The forecast for tomorrow looks on track. Dew points should be a degree or two higher than today (again due to evapotranspiration). When paired with highs in the mid to locally upper 90s, peak heat index values should range from 100 to locally 105F. While falling short of our Heat Advisory criteria of 105F, tomorrow will be a good day to practice heat safety.

Outside of the heat, all eyes tomorrow will be on the rapid southward expansion of near-surface smoke across the Great Lakes from the numerous wildfires burning in northern Minnesota and southwestern Ontario. Experimental HRRR and RRFS smoke data are ubiquitous in showing a wall of smoke expanding southward through Wisconsin and Michigan throughout the day and then crossing into northern and northeastern Illinois overnight into Thursday morning (including potentially off Lake Michigan). Interestingly, both advertise the leading edge of the near- surface smoke stalling somewhere near the I-88 or I-90 corridors by daybreak Thursday, presumably due to stagnating flow near the forecasted position of the center of a surface high pressure system. With that said, confidence in the southern edge of what should be a large area of smoke encompassing the Great Lakes region is naturally quite low.

Given the persistent model signal for smoke to make it into parts of our area, felt it was time to formally introduce such into the forecast Wednesday night through Thursday generally along and north of I-88 (so including the Rockford and Chicago metropolitan areas). With a similar model signal in smoke concentration to that on June 27, 2023, am concerned visibility during the Thursday morning commute could be reduced to just a mile or two where smoke is most prevalent. Note that the Illinois EPA is responsible for Air Quality Alerts, so will be watching for extensions in the current product that is valid through midnight Thursday. Finally, went ahead and proactively slashed high temperatures to top off around 80 degrees along and northeast of I-90 on Thursday where smoke should limit diurnal warming.

Updated products are out.

Borchardt

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 /00Z TAFS THROUGH 06Z THURSDAY/

Issued at 620 PM CDT Tue Jul 14 2026

Key messages for the 00Z TAF period:

* A lake breeze is expected to pass over the Chicago terminals and GYY on Wednesday

Light winds will favor a W direction through the night but may go variable at times. Winds will start out W on Wednesday before going E behind a lake breeze, less than 10 kt all the while. Wind shift is slated for early afternoon at GYY and mid- afternoon at the Chicago sites. Expect VFR throughout the period.

Doom

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 until 1 AM EDT Thursday for INZ019.

LM...None.