textproduct: Chicago

KEY MESSAGES

- Dangerous swimming conditions at unprotected beaches in Cook County and northwest Indiana today.

- Next chance for showers and thunderstorms towards midweek.

DISCUSSION

Issued at 219 AM CDT Sun Aug 23 2026

The broad upper troughing over the Great Lakes continues to shift east into the northeast CONUS this morning which is allowing a surface high to build into the region from the Upper Midwest. This surface high is expected to remain over the area through Tuesday which will result in rain-free conditions and comfortable humidity. However, the persistent north-northwest winds will keep temperatures on the seasonably cool side today and Monday with afternoon highs in the mid to upper 70s and overnight lows in the mid to upper 50s to locally near 60. Winds are forecast to become more southerly on Tuesday which should allow temperatures to rebound back into the 80s.

Speaking of winds, north-northwesterly gusts around 20 mph are expected this afternoon with locally higher gusts possible over the open waters of Lake Michigan. Despite ongoing breezy winds (10-15 kt) over the lake, waves have been rather slow to respond with current buoy observations showing 2.0-2.5 ft waves offshore of Cook County and 3.0-3.5 ft waves offshore of northwest IN. That said, as the north-northwest winds prevail it still looks as if wave heights should continue to increase through this afternoon resulting in an increasing risk for rip currents and dangerous swimming conditions, especially at northwest IN beaches. Therefore, the current plan is to maintain the ongoing Beach Hazard Statements for Porter, Lake (IN), and Cook Counties through this evening for this threat. So if you are planning to head to the beach today be sure to check the latest surf forecast beforehand and remember to stay dry where the waves are high!

Our next chance for rain is not expected until the middle of the week when the shortwave trough currently over the Pacific Northwest is forecast to pivot through the Great Lakes. Associated with the shortwave is also expected to be a cold front which will be the main driver of the anticipated shower and thunderstorm activity. The latest trend in the 00z guidance suite is for the front to begin to move into northern IL late Tuesday night with a decaying area of showers and thunderstorms along it. Given the late night arrival and the lingering mid- level dry air forecast to be overhead locally, it seems that the best coverage of any showers/storms Tuesday night will be near the IL-WI line. The front is then forecast to drift across northern IL and northwest IN on Wednesday which should allow for the redevelopment of showers and thunderstorms Wednesday afternoon and evening as diurnal destabilization occurs. While forecast soundings do show some decent MLCAPE values (around 1000-2000 J/kg) and steep mid-level lapse rates, the convergence along the frontal boundary looks to be rather meager which may limit the coverage of showers and storms on Wednesday. That said, forecast soundings also show around 25-35 kts of deep layer shear Wednesday afternoon which may allow a few storms to become strong to possibly severe. At this time our area is not outlooked for severe weather likely due to uncertainty in storm coverage and timing, but this will be a period to monitor as we get closer.

The cold front is forecast to exit the area late Wednesday night into Thursday morning which looks to allow another surface high to build into the area. Though, with some uncertainty as to how fast the front will exit this could change in subsequent forecasts. Regardless, another period of dry weather should develop to close out the work week, but there is a signal for more active weather to return towards the end of the weekend into the early part of the following week. On the bright side, temperatures do look to stay seasonable through the week with daily highs in the 80s and overnight lows in the 60s.

Yack

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 630 AM CDT Sun Aug 23 2026

Dry and VFR conditions are forecast through the period with diurnal cumulus developing around 6000 ft toward mid morning. Any lingering shower activity over Lake Michigan should remain east of the area. Light and variable winds early this morning will increase and settle into a prevailing NNW direction with the occasional gust into the upper teens to around 20 kt in the afternoon. A lake breeze will attempt to drift inland toward ORD/MDW early to mid afternoon and may stall near or right over MDW. However, confidence in it reaching either of the Chicago terminals remains too low to include with this update. Winds ease and become light and variable again after sunset then return to a prevailing NW direction after daybreak Monday.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through this evening for ILZ103-ILZ104.

IN...Beach Hazards Statement through this evening for INZ001-INZ002.

LM...Small Craft Advisory until 10 PM CDT this evening for the IN nearshore waters.