textproduct: Chicago

KEY MESSAGES

- Dry but cooler conditions today and Thursday, followed by increasing rain chances Friday.

- Intermittent shower/thunderstorm chances for Memorial Day weekend, though much of the period should be dry.

- Several periods of moderate to high swim risk conditions possible from today through early next week due to persistent northeast winds over Lake Michigan.

DISCUSSION

Issued at 314 AM CDT Wed May 20 2026

Mainly dry, breezy and cooler weather conditions are expected today through Thursday, in the wake of yesterday's cold frontal passage. Early morning surface analysis shows this front now extends from western Lake Erie to far southern Illinois along the Ohio River. Have noted a few spotty sprinkles as far north as the Pontiac-Rensselaer areas overnight, likely where lingering moist advection was still occurring within the elevated baroclinic zone north of the surface front. These will end prior to sunrise however, as the southern periphery of a mid-level short wave trough passes east of the region. Farther northwest, 1026 mb surface high pressure was centered near Sioux Falls this morning, and is progged to build east-northeast across the upper Great Lakes region by tonight. This will result in our north-northwest winds shifting northeast and becoming breezy by midday/afternoon with gusts near 20 mph (around 25 mph near/downwind of Lake Michigan into northeast IL/northwest IN). Temperatures, after being in the 70s and 80s over the past several days, will be limited to the low-mid 50s along the Lake Michigan shore, and the low-mid 60s well inland beneath partly to mostly cloudy skies. With the breezy northeast winds and building waves on the lake, have issued a Beach Hazard Statement for the Illinois and Indiana shores today into Thursday.

Overnight lows tonight may dip to around the 40 degree mark along the IL/WI border, and in the low-mid 40s elsewhere with partly cloudy skies. Thursday will be similar, though with more easterly winds and slightly milder temperatures in the mid-upper 60s well west and south of the lake-cooled areas of northeast IL and far northwest IN.

Clouds look to spread in from the west late Thursday/Thursday night, ahead of a mid-level short wave lifting northeast from the southern Plains and the base of a western CONUS upper trough. An associated surface low pressure wave is progged to track into the lower Missouri Valley by late Thursday night, then slowly track northeast across central IL/northern IN Friday into Friday night as the short wave transits the region. This is expected to spread rain/showers across the area during this time, though there remains some guidance/ensemble spread as to the northward extent of the rain shield into our antecedent dry low-level air, though rain chances increase across much of the area by Friday afternoon and evening. Thunder potential looks quite low, with the forecast MUCAPE reservoir forecast to remain largely south of the cwa. Cloud cover, rain and enhanced E-NE surface winds north of the low track will make for another cool day Friday with highs again in the 50s near the lake and low-mid 60s elsewhere. Rain should taper off overnight Friday night as the mid-level and surface waves pass.

Medium-range ensembles depict the aforementioned western upper trough tracking slowly across the Midwest through Sunday, eventually shifting east of the region Monday/Tuesday. While this may maintain at least some threat of intermittent showers over the holiday weekend, current guidance suggests that there will likely be many dry daytime hours. A gradual warming trend is also depicted Saturday into Tuesday with daytime temperatures forecast to warm back into the 70s/possibly 80s.

Ratzer

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1238 AM CDT Wed May 20 2026

No major forecast concerns for the terminals for this TAF period.

Mid-level cloud cover continues to stream over the Chicago area terminals associated with a plume of moisture on the backside of a elevated frontal zone. While BKN to OVC 10000-15000 ft ceilings are expected to linger overnight (especially at GYY), skies will scatter out around daybreak as high pressure builds into the area. VFR conditions will prevail for the rest of the forecast period. Winds will remain breezy out of the northwest tonight with occasional gusts in the upper teens. Directions will become northeasterly around 12-13z Wednesday and remain as such for the rest of the TAF cycle with speeds in the 10-15 kt range with occasionally higher gusts through Wednesday evening before speeds ease into the 8-10 kt range.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 10 AM this morning to 10 AM CDT Thursday for the IL nearshore waters.

Small Craft Advisory from 7 AM this morning to 7 AM CDT Thursday for the IN nearshore waters.