textproduct: Chicago

KEY MESSAGES

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

- Chance of thunderstorms with possible heavy rain and localized flooding Wednesday into early Thursday.

DISCUSSION

Issued at 216 PM CDT Sun Aug 2 2026

Relatively quiet weather conditions with seasonably cool temperatures are expected for the next couple days as mid-level ridging edges northeastward across the Great Lakes region. Uncharacteristic of early August, low stratus with embedded patches of drizzle continue to filter over northeast Illinois this afternoon in response to abundant moisture trapped under the incoming subsidence inversion. Given a persistent corridor of upstream low-level clouds over central Lake Michigan, saturated ground conditions from Saturday's heavy rain, and clearing skies aloft, have some concern that low-level stratus (possibly lowering to the ground as fog) will expand southwestward under the inversion overnight. Have accordingly increased cloud cover and added patchy fog for a large portion of the CWA during this time. Otherwise, dangerous swimming conditions will continue into Monday morning before winds gradually diminish.

Late Tuesday night through Thursday, a large upper-level low over southern Hudson Bay will push a slowing/stalling cold front near or over the CWA. A seasonably strong kinematic environment highlighted by a 100+ knot upper-level jet across the far Upper Mississippi River Valley has the making for a drawn out precip event with a mix of warm season convection and cool season anafrontal elements. Adding in a well-timed passing mid-level shortwave interacting with a very moist airmass (PWATs nearing 2 inches), will need to monitor for a non-zero severe storm risk, and especially renewed flooding potential Wednesday into early Thursday.

Low-level WAA and moisture advection will quickly return by early next weekend while a broad low-amplitude ridge drifts across the western CONUS. Expect summerlike warmth and increasing humidity for the weekend. Building instability and modest WNW flow aloft will also support increasing chances for convective episodes into the Great Lakes region by Sunday.

Kluber

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1237 PM CDT Sun Aug 2 2026

Key Messages:

- MVFR cigs improving/scattering later this afternoon then clearing this evening.

- North-northeast winds gusting 20-25 kt at times this afternoon then diminishing this evening.

- Potential for some mist/fog and low stratus late tonight/toward daybreak well inland of Lake Michigan, IFR possible.

The terminals remain between departing low pressure to the east and approaching high pressure from the northwest early this afternoon. BKN-OVC stratocu deck persists with mainly MVFR conditions underneath. Earlier pockets of IFR ceilings and mist/drizzle have largely improved or dissipated. Ceilings will gradually lift and scattering of the MVFR deck will occur through the afternoon. Breezy north-northeast winds will continue with some occasional gusts into the 20-25 kt range, especially at ORD, MDW and GYY.

Winds will diminish this evening as high pressure settles into the area. Skies will clear but moist ground, light winds, and abundant low level moisture point toward fog/mist potential inland of Lake Michigan toward daybreak. Have added MVFR visibility and SCT low clouds at RFD and DPA for a few hours early tomorrow morning. Will need to continue to assess this as IFR may develop with cigs of 005 or less and visibility potentially below 1SM. Improvement would occur mid morning. Otherwise, expect light east winds Monday with VFR expected, though may need to added some FEW-SCT diurnal clouds toward midday.

MDB

LOT WATCHES/WARNINGS/ADVISORIES

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

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

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