textproduct: Chicago

KEY MESSAGES

- Rain expected to develop during the day Friday, continue into Friday night, before ending Saturday. Widespread rainfall totals over an inch are possible.

DISCUSSION

Issued at 140 AM CDT Wed Jul 29 2026

Quiet weather expected through Thursday night with seasonably warm temperatures and very comfortable humidity levels. Lake breezes both today and tomorrow will result in some modest cooling right along the lakefront. While skies should be sunny today, wildfire smoke aloft will likely filter the sun some.

Guidance continues to bring a strong northern stream shortwave trough into the Midwest Friday. Our area will remain on the cool side of the developing surface low, so the better instability and thunderstorm chances should remain south of our CWA. However, strong synoptic ascent and seasonably high PWATs could allow for a pretty good soaking for areas that end up under the deformation zone rain Friday night, which looks to be most of our CWA. The cloud cover and developing rain on Friday should result in below average temps; mostly in the 70s, except lower 80s eastern most CWA where rain will arrive last.

Lower confidence in the forecast details Saturday as there is spread in guidance in how quickly this system moves out. Medium range guidance has trended away from cutting off a mid-upper level low that meanders around the region and now is more progressive pushing the trough southeast of the area. Timing of the trough's departure will impact rain chances and temperatures over the weekend. Given the lower than average forecast confidence, no changes were made to NBM which maintains cooler temps and rain into Saturday. If guidance continues to trend quicker, then later Saturday and especially Sunday could end up dry. Next week looks to start dry and seasonably warm.

- Izzi

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 619 AM CDT Wed Jul 29 2026

Quiet, primarily VFR flying conditions can be expected through the period, with north to northeast winds today (near/around 10 kt this afternoon near the lake), becoming light/VRB to calm this evening. There's a signal for some reduced VSBY in BR across parts of interior northern IL Thursday morning. Opted to include TEMPO MVFR VSBY for RFD and may need to consider adding a TEMPO to DPA with later issuances.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement until 10 AM CDT this morning for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement until 10 AM CDT this morning for INZ001-INZ002.

LM...Small Craft Advisory until 7 AM CDT this morning for the IL and IN nearshore waters.