textproduct: Chicago

KEY MESSAGES

- Warmer and more humid conditions are expected late this weekend into next week, with a couple chances for thunderstorms.

DISCUSSION

Issued at 144 PM CDT Wed Aug 26 2026

A cold front extending from the Kankakee River Valley in northwest Indiana to just northwest of Champaign will continue to generate a broken line of thunderstorms over the next hour or so before exiting to the east. Brief instances of large hail and damaging wind remain possible. Farther northwest, low-level mixing and some mid-level warming is gradually reducing MLCAPE behind the front. While isolated showers remain possible as a weak trailing mid-level wave drags across northern Illinois this afternoon, latest trends favor primarily dry conditions.

High pressure will build across the western Great Lakes on Thursday before drifting eastward Friday and Saturday. Precip- free conditions are expected during this time with the exception of isolated showers or sprinkles on a lake breeze boundary across northeast Illinois Thursday afternoon.

A loosely zonal pattern transitioning to low-amplitude ridging across North America this weekend into the middle of next week favors a more active storm track north of the forecast area. WAA and an embedded mid-level wave on the leading edge of the ridge Saturday night into Sunday morning may result in convection extending as far south as northern Illinois. Otherwise, summer warmth will return with increasing humidity and daytime highs pushing well into the 80s, and possibly low 90s, if the active storm track does remain north of the area.

Kluber

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1247 AM CDT Thu Aug 27 2026

Forecast concerns for the terminals...

- Patchy fog possible near the Kankakee River Valley tonight.

- Lake breeze to result in an easterly wind shift at Chicago area terminals Thursday afternoon.

High pressure continues to settle into the Midwest and is expected to remain in control over our weather through the TAF period. Therefore, expect light northwest winds around 5-10 kts to prevail through much of the period, though a lake breeze will result in an easterly wind shift at ORD, MDW, and GYY Thursday afternoon. Guidance is in generally good agreement on the lake breeze arriving at ORD and MDW between 19z and 21z (around 16-17z at GYY) but as is typical suspect some shifts in timing may occur as we get closer. Winds will then become more light and variable Thursday night as the center of the high passes overhead. Otherwise, expect VFR conditions to prevail through the forecast period.

While there is a chance (15-20%) for some shallow fog (3-5 mile visibilities) to develop near and south of the Kankakee River Valley tonight, it seems any fog should remain generally south of the TAF sites. Finally, there is also a non-zero (10-15%) chance for an isolated shower to develop along the lake breeze Thursday afternoon. Given that moisture depths are somewhat shallow confidence on shower coverage is too low to warrant a TAF mention, but did introduce a BKN050 mention to the Chicago terminals and GYY to tease this potential.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

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