textproduct: Chicago

KEY MESSAGES

- Chance of thunderstorms returns Wednesday, some possibly becoming strong in the afternoon. Periodic, but low, chances for storms then continue through the end of the week into the weekend.

- Turning hotter and more humid into early next week.

DISCUSSION

Issued at 211 PM CDT Tue Jun 23 2026

Main forecast concern is thunderstorm chances Wednesday into Wednesday night as an upper level trough and associated surface low moves across the Great Lakes region. Showers and scattered thunderstorms across MN are expected to continue moving southeast into south/central WI tonight. There is still quite a bit of uncertainty regarding how far south this activity may move, possibly reaching far northern IL in the predawn hours with a bit better chance for at least showers across northern IL Wednesday morning. As a cold front moves across the area Wednesday afternoon into Wednesday evening, scattered thunderstorms will be possible and while instability may be limited, the wind field is sufficient for any organized storms to possibly become strong to severe and trends will need to be monitored.

Models are slowly trending further south with precip chances for Thursday and Friday, though still chances across the southern cwa, especially later Friday into Friday night. There will still be a chance for showers and thunderstorms over the weekend as the upper ridge builds across the area. The best timing continues to fall in the Saturday afternoon to Sunday afternoon time frame, with perhaps the best chance now looking to be in the late Saturday night/early Sunday morning time period. Quite a bit of uncertainty, but it will need to be monitored for possible strong storms/heavy rain.

The ridge then builds into the region Sunday into Monday with warmer and more humid air spreading across the region with highs on Sunday likely in the upper 80s and lower 90s on Monday. While much of next week currently appears to be very warm/hot and humid, there are concerns for how close the local area will be to the edge of the ridge and for how close thunderstorm activity may evolve, especially by Monday night into Tuesday, which could have large impacts on temperatures. cms

AVIATION /00Z TAFS THROUGH 06Z THURSDAY/

Issued at 651 PM CDT Tue Jun 23 2026

Aviation forecast concerns for the 00Z TAFs:

- Easterly lake breeze winds become southeast this evening, with southwest winds gusting 15-20 kt at times on Wednesday.

- Periods of SHRA likely by mid-late morning, with scattered TSRA possible Wednesday afternoon/early evening.

Surface high pressure was over the western Great Lakes region early this evening, supporting modest lake breeze winds off of Lake Michigan. These east-northeast winds will diminish and become light southeast through the evening, before eventually turning light south-southwest predawn Wednesday as the surface high pressure ridge drifts away to the east.

An area of low pressure currently over the upper Midwest (ND/MN border region) will track east across WI on Wednesday in association with a mid-level disturbance, and will trail a weak cold front across the terminals later Wednesday night. Scattered showers are expected to spread across southern WI and the IL/WI border region around/after daybreak Wednesday, in a region of modest but persistent warm/moist advection. These showers will likely eventually spread southeast across the terminals during the early to mid-morning hours and persist into the afternoon. Thunder potential initially appears low (less than 30%), but does look to increase during the afternoon during peak diurnal warming. Some detail/coverage/timing differences remain in high- res model guidance, though convectiion-allowing ensembles focus highest thunder chances (~40%) after ~20Z at KRFD and after ~22Z in the Chicago metro area. Have indicated prevailing VCSH and PROB30 TS mentions in the TAFs for now, though if confidence increases could see the need for TEMPO mentions with later forecasts.

Otherwise, VFR conditions are expected, with winds becoming southwest with gusts 15-20 kt during the day Wednesday.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

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