textproduct: Chicago

KEY MESSAGES

- Quieter conditions with near to slightly above normal temperatures through the weekend.

DISCUSSION

Issued at 114 PM CDT Thu Sep 10 2026

Through Sunday Night:

Ongoing rain showers are being observed south of the Kankakee River Valley this afternoon ahead of a mid level wave that is passing over the area. There has been an increase in shower coverage over the area, being located under the right entrance region of a 300 mb jet. However, lapse rates are fairly poor with the better well of instability south of the forecast area. A rogue lightning strike or two may occur, but confidence is low. This mid level wave should continue to pass south and east over the forecast area through the afternoon with chances for showers diminishing toward sunset.

Cloud cover over the area today has help mute temperatures slightly. Clearing behind the wave should allow for temperatures northwest of the Fox Valley to increase quickly, but opted to lower this afternoon's high temperatures else by a degree or two. As the wave exits to the east, clearer skies can be expected through the overnight north of I-80 (with lingering cloud cover to the south). Winds are expected to become light and variable overnight. With better radiational cooling due to the lack of cloud cover, there is a chance for another round of fog to develop toward daybreak tomorrow morning. Better chances remain north and west of Chicago's urban core, but satellite and observations will need to be monitored through the night for any fog development.

Surface high pressure will build tomorrow under the influence of a weak ridge passing overhead. Sunny conditions are expected with light winds to provide quite an ideal weather day tomorrow. As the ridge passes east overnight into Saturday morning, models are projecting a very weak shortwave to pass over Wisconsin. There is a non-zero chance that there could be some light showers/sprinkles on Saturday morning as the wave passes over, but models are a.) keeping the track of the wave a little farther north in Wisconsin and into western Michigan and b.) struggling to penetrate a drier air mass over Illinois. Models are suggesting that the surface cold front associated with the wave could potentially slow and wash out over I- 80 by Sunday morning. Perhaps some light showers develop along the front on Sunday morning, but again, the drier air and weak forcing should limit coverage, assuming it happens at all. Otherwise, this weekend is looking fairly pleasant. Southerly winds on Saturday will help drive temperatures back up into the 80s. There is a little more uncertainty with temperatures on Sunday due to the timing of the frontal passage. An early arrival will turn winds to the northwest and usher in cooler, more seasonable temps in the 70s. But areas ahead of the front south of I-80 have another chance of warming back up into the 80s.

DK

Monday through Thursday:

The first half of next week continues to look like it will turn more active as we get into more of a southwesterly flow aloft. There will be multiple opportunities for showers and thunderstorms Monday-Wednesday as several shortwave troughs ripple through the southwesterly flow. It remains too early to pinpoint timing or rainfall amounts, but there is better chances for a transition to a generally wetter, more unsettled pattern next week.

Izzi/DK

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1243 PM CDT Thu Sep 10 2026

There are no significant aviation forecast concerns for the terminals at this time.

Light winds and clearing skies tonight may allow for fog to develop in some spots once again tonight into Friday morning. Confidence remains low in the coverage of this fog and whether it will affect any of our TAF sites, though it would primarily be a concern for RFD, DPA, and/or GYY if it were to occur. Light flow within a region of surface high pressure and sharpening lake breezes both this afternoon and again tomorrow lends lower-than-average confidence in precise wind direction trends. That said, winds should largely remain under 10 kts with wind directions likely to retain an easterly component through most of the TAF period at ORD and MDW.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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