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 /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1236 AM CDT Mon Aug 3 2026

The primary forecast concern is the potential for low clouds and fog through mid morning.

Light winds and moist low levels are expected to allow fog to form outside of the Chicago terminals overnight with dense fog possible southwest of RFD and south of GYY. Ifr/lifr cigs are also possible across the area overnight into Monday morning, before lifting and scattering out. Overall confidence for these trends is only medium and previous forecast looks reasonable at this time.

Light northerly winds will likely become light and variable for most areas overnight and may remain light and variable through midday Monday when a general southeasterly direction is expected. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement until 3 AM CDT early this morning for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement until 9 AM CDT this morning for INZ001- INZ002.

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