textproduct: Chicago

KEY MESSAGES

- Potential for an increased fire danger on Thursday due to unseasonably warm, dry, and breezy conditions.

- Periodic shower and thunderstorm chances return Friday into Saturday and potentially into early next week.

DISCUSSION

Issued at 200 PM CDT Wed Jun 3 2026

An upper level ridge, the central piece of an omega blocking pattern over the CONUS, is projected to break down and slowly move east through the end of the week. As this begins to occur overnight tonight, broad southwesterly flow is expected to slowly advect increasing moisture into the region. For tonight and tomorrow, its main impact will be on increasing mid and high level cloud cover. Despite these clouds, warmer air will continue to advect in driving high temperatures tomorrow into the mid 80s reaching all the way to the Lake Michigan shoreline. Low level dry air will drop relative humidities down into the 20 percent range. With model soundings showing efficient mixing, southwest surface winds are expected to become breezy with gusts up to 25 mph. With the input from our local fire partners commenting on the dry fuels around the area due to the lack of wetting rainfall recently, there is the potential for an elevated grass and brush fire danger setup for tomorrow.

As the ridge breaks down, a series of upper level shortwaves will pass over the forecast area providing the next chances for showers and storms. An initial lead wave is expected to move in Friday morning and pass through the day. While cloud cover could play a factor in reducing instability, showers and storms that develop closer to the better forcing could potentially send some outflow into the forecast area helping increase coverage. While widespread severe storms are not expected, cannot rule out some damaging wind gusts with any isolated stronger storm that develops, though the better chances are in northwest Illinois. While the higher water content looks to remain north of the area, p-wats around 150 percent of normal leads to the potential for isolated downpours. With drier antecedent conditions, widespread flash flooding is not expected, though ponding on roadways and low lying areas is possible.

The longer upper level wave is expected to move over and east of the area on Saturday and another upper level ridge forms over the central Plains. As it does, a surface cold front will move south over the forecast area. Models are disagreeing on the speed and distance southward that this boundary will move. So there is lower confidence in when rain will end on Saturday, though generally drier conditions are expected around and after sunset. There is a non-zero chance that the front becomes quasi- stationary by Sunday morning around or just south of US-24. Blended PoPs kept a slight chance for rain in the southwestern part of the forecast area on Sunday, with better chances in west-central Illinois.

There is the chance for another short wave trough embedded in the western side of the ridge to move northward over the Central Plains early next week. Confidence is low in the chance that this wave brings precipitation to the region, given that most models are suggesting it phases with an upper level trough over the Intermountain West as a pseudo omega block tries to form once again over the CONUS. As moisture sloshes northward, there are additional chances for showers early next week. But as the ridge of the block strengthens over the eastern CONUS, warmer and drier conditions are currently projected by midweek.

DK

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1250 PM CDT Wed Jun 3 2026

Key aviation forecast messages:

- Winds may vary from SSW to SSE at times near the lake breeze this afternoon - Breezy SW winds around 20 kt develop after daybreak Thursday

VFR and dry conditions are expected through the TAF period. Wind directions early this afternoon continue to vary from SSW to SSE and is most pronounced near the lake breeze boundary which has stalled just east of ORD and MDW. The boundary is expected to gradually push farther inland with time through the afternoon, though confidence in when it reaches the terminals (and where it ultimately stalls again) remains low. Have maintained the 21Z timing for the return to prevailing SE winds for now at those sites. Winds become light and variable after sunset this evening and overnight, eventually settling back into a prevailing southwest direction late tonight. Winds then become increasingly gusty after daybreak on Thursday, with peak gusts around 20-25kt in the afternoon.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

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