textproduct: Chicago

KEY MESSAGES

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

UPDATE

Issued at 834 PM CDT Thu Sep 10 2026

Evening forecast adjustments made for ending precip, and fog potential overnight.

Several lingering boundaries (cold front, lake breeze and differential heating) became the focus for scattered convective showers this afternoon, also producing a few funnel clouds between I- 80 and U.S. 24. All of that activity has dissipated with the loss of diurnal instability at sunset. Attention for the overnight and early morning hours then shifts to fog/low stratus potential, as the western periphery of a surface high pressure ridge settles across the area. Most likely area to be affected is across our southern cwa where low-level moisture lingers in the wake of the southward drifting cold front, and where cloud cover and earlier precipitation had limited warming/mixing. Guidance does depict some low-level drying later tonight across our southeastern counties however, as high pressure centered east of the area develops northeast winds and dry advection above the boundary layer. Have expanded patchy fog mention after midnight tonight for areas well west/south of Chicago based on this (and where a variety of high-res guidance depicts lower visibilities) and will continue monitor trends. Can't rule out some dense fog potential across mainly our south/southwestern cwa.

Otherwise, only made tweaks to temps/sky cover based on observational trends overnight, with a period of quiet and pleasant weather expected Friday.

Ratzer

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 /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 635 PM CDT Thu Sep 10 2026

The only forecast concern this period is the potential for fog early Friday morning. Confidence is too low for any mention of fog in the terminals, with a low chance for fog at RFD and then better chances west and southwest of the terminals.

Easterly winds generally under 10kt are expected to become light and variable later this evening and then become southeast under 10kt Friday morning, with speeds possibly increasing to 10-12kt by mid/late Friday afternoon. cms

LOT WATCHES/WARNINGS/ADVISORIES

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