textproduct: Chicago

KEY MESSAGES

- Showers and embedded thunderstorms will gradually shift south and east through tonight and may cause localized flooding.

- High waves and dangerous swimming conditions will continue at unprotected Lake Michigan beaches through Monday morning.

DISCUSSION

Issued at 306 PM CDT Sat Aug 1 2026

A baggy slow moving surface low centered over central Illinois continues to very slowly drift across the region this afternoon with spiraling bands of showers and some embedded thunderstorms wrapping around the system. The key forecast question for much of the day has been where the heaviest bands of rain would set up and begin to pivot this afternoon. The slow moving nature of the system paired with elevated PWATs and warm rain processes has been supportive of rainfall rates in excess of 1-2"/hr at times. Even seemingly "lighter" radar reflectivity values are still likely producing heavy rainfall. Based on the latest radar trends there are two separate general corridors ongoing at this hour. The first extends along the I-80 corridor that is very gradually rotating counterclockwise. This is leading to a slight northwest propagation of the northern periphery into central Cook and Chicago. It is unclear how far north this reaches over the next few hours but can't rule out heavy downpours and a few lightning strikes as far north as downtown (20-30 percent chance) through late afternoon. A gradually broadening of those band of showers has helped lower the rainfall rates some over the past 15-30 minutes at least.

The second axis extends from near Pontiac southeast into central IL/IN but has similarly broadened with localized pockets of heavier rates. Earlier concerns of funnel clouds and possibly brief landspout have eased for now due to weaker low- level instability lifting this far northwest compared to what model guidance had depicted earlier in the day. It will still be worth monitoring over the next few hours into portions of Iroquois, Ford, and Benton Counties, especially if any clearing occurs within the broader cloud layer.

A Flash Flood Watch remains in effect until 7 PM CDT for Cook, DuPage, Will, Grundy, and Livingston Counties to account for the ongoing heavy rainfall though the threat of widespread flooding appears to be waning some. This axis should gradually shift south and east with time into this evening where the Flash Flood Watch remains in effect for all of northwest Indiana and Iroquois/Kankakee/Ford Counties in Illinois through 1 AM CDT.

Persistent gusty onshore winds will lead to continued high waves and dangerous currents along the lakeshore and at Lake Michigan beaches through Monday morning. Stay dry when the waves are high!

In the wake of the departing surface low, upper ridging and surface high pressure moves back into the region leading to mainly dry conditions for the first part of the upcoming week. An upper level shortwave will move across the Upper Midwest toward midweek which may swing a cold front through the region and bring shower and storm chances back to the area. Confidence in the details decreases thereafter though additional waves may move within the broader northwest flow at times through the end of the week.

Petr

AVIATION /00Z TAFS THROUGH 06Z MONDAY/

Issued at 620 PM CDT Sat Aug 1 2026

Showers will gradually diminish this evening as an area of low pressure steadily shifts southward. Low-MVFR to near IFR cigs will persist this evening at the Chicago-area terminals. There is some potential for VFR to return for a brief period late this evening, but given the current expected brief nature, elected to simply prevail MVFR conditions through the night and Sunday morning. Will offer AMDs if VFR looks to become more expansive.

At RFD: VFR has returned and is expected through much of the evening. Decent signal in the guidance for low-MVFR, possibly IFR cigs to develop to the north and push across the airfield late tonight into early Sunday morning. There is also some threat for BR if clearing if sufficient to allow temperatures to cool this evening. Confidence is too low in this to offer anything more than 6 SM BR at this point.

Otherwise, VFR will return to all TAF sites Sunday afternoon. Strong and gusty northeasterly winds will diminish a bit late this evening, but gusts will continue through Sunday before winds finally ease Sunday evening.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through Monday morning for ILZ006- ILZ103-ILZ104.

Flood Watch until 7 PM CDT this evening for ILZ013-ILZ020- ILZ021-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Flood Watch until 1 AM CDT Sunday for ILZ023-ILZ033-ILZ039.

IN...Beach Hazards Statement through Monday morning for INZ001- INZ002.

Flood Watch until 1 AM CDT /2 AM EDT/ Sunday for INZ001-INZ002- INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 3 AM CDT Monday for the IL and IN nearshore waters.