textproduct: Chicago

KEY MESSAGES

- Periodic shower/storm chances over the weekend and into early next week

- Heat and humidity is expected to increase next week

DISCUSSION

Issued at 121 AM CDT Fri Aug 28 2026

Winds have gone calm over much of the forecast area this morning. Clearer skies west of the Fox Valley have helped drop dew point depressions down to between 2 to 4 degrees (at the time this discussion was published), whereas lingering clouds above 5,000 feet have kept much of the Chicago Metro area drier. Reduced visibility is possible this morning, but confidence is lower for the Metro. The better chances for patchy fog to develop around daybreak looks to be around and west of the Fox Valley or near and south of the Kankakee River Valley

GOES water vapor satellite imagery this morning shows a upper level trough over the northern Great Lakes slowly moving east, as a ridge spreads northward over the intermountain west (including a stout MCS moving south down the lee side of the ridge into Kansas). That ridge will be the focus for the rest of the forecast; but, for today, surface high pressure will create fairly quiet weather conditions locally. High temperatures are expected to be in the low 80s, with a weak lake breeze developing in the afternoon.

The ridge is expected to expand eastward tonight and into Saturday. This will allow slight perturbations in the height field to move eastward over the weekend. The point of uncertainty is where will the ridge axis set up and if the shape of the ridge will make it more favorable for showers and storm to move into Illinois. For now, models are suggesting a short wave trough will move through the upper level pattern Saturday afternoon through the overnight. Models are still suggesting that the EML plume should be more focused over southern Wisconsin, but there will be plenty of warm air advection and steepening lapse rates through the afternoon and evening for the chances of showers and storms to develop. Model trends will need to be monitored to get a better sense on coverage and any southern terminus for showers/storms.

That ridge is expected to continue to expand eastward Sunday and through the next week. No major changes were made to the PoPs the NBM provided as slight/chance wording certainly fits the bill for any "ridge rider" that might pass over the area. More notably is global and ensemble guidance increasing 850 mb temperatures above 20C by the middle of next week. With dew points increasing into the low 70s, there is a chance for heat indices to increase into the upper 90s. September might be approaching, but summer is far from over.

DK

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1237 PM CDT Fri Aug 28 2026

The only forecast concern is a possible lake breeze/wind shift this afternoon. Currently, a lake breeze is just inland near Lake Michigan. Confidence is low for how far west this lake breeze will continue to move and trends will need to be monitored. Otherwise, light south/southwest winds will continue through tonight, possibly becoming light and variable tonight. South/southwest winds will increase into the 10-12kt range by midday Saturday with gusts into the 15-20kt possible Saturday afternoon. Wind directions are expected to become more south/southeast late Saturday afternoon into Saturday evening, when gusts are expected to diminish.

There is a small chance for a few showers mid/late Saturday afternoon, mainly across far northern IL. The low levels will remain fairly dry which may allow for only some sprinkles or virga. cms

LOT WATCHES/WARNINGS/ADVISORIES

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