textproduct: Chicago

KEY MESSAGES

- Seasonably warm conditions through Monday, although cooler and more comfortable than recent days.

DISCUSSION

Issued at 114 PM CDT Sun Sep 6 2026

Surface high pressure continues to expand over the Great Lakes early this afternoon, providing the area with cooler east- northeasterly surface winds. While dewpoints started the day around 70, a persistent influx of a drier low-level airmass has continued to drop values through the 60s this morning. The remainder of the day will be rather pleasant, with mostly sunny conditions and temperatures peaking from around 80 inland to the mid and upper 70s closer to the lake. Similar conditions are expected for Labor Day, as the Great Lakes surface high remains dominant.

East-northeasterly onshore winds across southern Lake Michigan are not terribly strong (10-15 knots). However, the fetch has allowed waves to become choppy across southern Lake Michigan, with wave heights generally in the 2 to 4 foot range along the northeastern Illinois shores. These conditions are expected to persist tonight, making for a Moderate Swim Risk at northeastern Illinois Lake Michigan beaches.

Late Monday into Tuesday, the mid/upper Pacific Northwest trough/low is expected to eject east-northeastward across the northern Rockies. As it does, models and ensembles remain in general agreement regarding the development and northeastward shift of a seasonably strong surface low across Manitoba. While this system will remain far removed from our area, it will act to drive the mid-level ridge axis residing over the Plains back eastward into the western Great Lakes for Tuesday. An accompanying shift back to southerly low-level flow will thus result in warming weather across our region into midweek. Temperatures for Tuesday into Wednesday are expected to climb back well into the 80s (potentially near 90 in some locations). Humidity will also be on the increase, though it is not expected to reach the magnitude experienced a couple of days ago.

This period of warmer weather is expected to remain short- lived, as the cold front associated with the potent Canadian low begins to sag southward across our area Wednesday into early Thursday. A period of showers and thunderstorms will be possible (50%+) with this front from late Tuesday night through Wednesday night. However, the better synoptic-scale forcing does not look to coincide with the surface front until potentially later Wednesday night into Thursday morning. By this time, the front should be shifting south of much of our area into central Illinois and Indiana. For this reason, shower and thunderstorm activity could remain more scattered in coverage in our area on Wednesday.

Surface high pressure will build back into the region for Thursday and Friday in the wake of Wednesday's cold frontal passage. This will result in a return to cooler, more pleasant weather through the end of the workweek. As we head into next weekend, there is a signal for a larger-scale mid-level trough and surface cold front to shift into the central CONUS later in the weekend. However, specifics regarding the pattern remain largely unclear at this time owing to increasing ensemble spread. Nevertheless, chances for showers and thunderstorms return to the forecast for next weekend.

KJB

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 630 PM CDT Sun Sep 6 2026

No significant aviation weather concerns for this TAF period. The forecast area will remain within the western periphery of expansive surface high pressure drifting slowly southeast across the Great Lakes region through Monday night. While there may be some light/variable winds during the night away from the Chicago metro, the pattern will generally maintain modest easterly winds (with a slight afternoon lake-breeze push for ORD/MDW/GYY), with VFR conditions (mainly high cirrus from convection well west/northwest of the area) prevailing.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

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