textproduct: Chicago

KEY MESSAGES

- Isolated to widely scattered shower or storm possible (15-20% chance) this afternoon, mainly near Lake Michigan.

- Dangerous swimming conditions expected at Porter County Lake Michigan beaches today, then at all Indiana and Cook County Lake Michigan beaches late tonight and Sunday.

DISCUSSION

Issued at 236 AM CDT Sat Aug 22 2026

A cold front is currently analyzed roughly from a Chicago to Galesburg line early this morning and is continuing to slowly drift south and east out of our forecast area. Generally speaking the better shower and thunderstorm coverage ahead of the front has been in central IL, but a couple of showers have been festering in southern Newton, Jasper, and Benton counties. These showers may briefly produce a rouge lightning strike prior to exiting these areas over the next hour, but otherwise dry conditions are expected for the rest of the night.

In the wake of the cold front, winds will become northwesterly and gradually increase in speed through the morning with gusts expected to peak around 20-25 mph (locally up to 30 mph) this afternoon. These northwest winds will build waves on Lake Michigan today and result in dangerous swimming conditions, especially into Porter County, IN beaches. As wind directions become more northerly tonight, the large waves are forecast to pivot westward into Lake (IN) County and Cook County beaches overnight tonight and will persist through Sunday evening. As a result, a Beach Hazard Statement remains in effect for Porter County, IN starting at 10 AM today and lasting through Sunday evening with new Beach Hazard Statement issued for Lake (IN) and Cook Counties starting late tonight through Sunday evening. If planning to head to the beach today make sure to check the surf conditions and remember to stay dry when waves are high!

Aside from the breezy north-northwest winds today, mostly dry conditions are expected as drier air filters into the region. However, broad upper troughing over the Great Lakes is expected to linger through much of today and will allow the shortwave trough in northern WI to pivot overhead this afternoon. While overall moisture looks to be meager to say the least, forecast soundings continue to show some modest instability and some low- level moisture lingering near Lake Michigan which may be sufficient to kick off isolated to widely scattered showers and perhaps a thunderstorm this afternoon (15-20% chance). That said, no severe weather is expected today and any showers/storms that do develop should wane around or shortly after sunset. Otherwise, expect mostly to partly cloudy skies with seasonably cool temperatures in the upper 70s to around 80 degrees.

The upper troughing will gradually shift into the eastern Great Lakes tonight as high pressure builds into the Midwest. This will result in completely rain-free conditions for Sunday, Monday and most likely Tuesday. However, continued northwest flow will keep temperatures on the cooler side for this time of year with highs Sunday and Monday in the mid to upper 70s and overnight lows in the 50s to around 60. Temperatures are forecast to moderate a bit on Tuesday as winds turn more southerly, but highs still look to top out in the upper 70s to lower 80s at best.

While we enjoy a well deserved break in the weather, another shortwave trough is forecast to be traversing across the Pacific Northwest and Northern Plains early next week before pivoting into the Great Lakes towards the middle of the week. Guidance continues to show that a cold front should develop ahead of this shortwave and is progged to move through the region sometime during the Wednesday to Thursday timeframe. While there is overall good agreement on this evolution amongst ensemble and deterministic guidance, there is a lot of uncertainty around when exactly the wave and associated front will arrive in northern IL and northwest IN thus making this part of the forecast lower confidence. Bottom line expect to see increasing shower and thunderstorm chances towards the middle portion of next week and keep checking back for more specifics as we get closer in time. Though, temperatures should also be increasing towards more typical late August readings ahead of this system too.

Yack

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1227 PM CDT Sat Aug 22 2026

A few isolated showers and perhaps an isolated thunderstorm are possible this afternoon, primarily east of the Chicago terminals. If confidence increases in coverage, then TAFs may need to be amended to include a VCSH for a few hours this afternoon. Otherwise, look for VFR conditions through the TAF cycle.

Northwest winds will gust to around 20 mph this afternoon, likely easing and losing gustiness as sunset approaches. Lake breeze will develop this afternoon and move through GYY resulting in a wind shift to lighter NE. Lake breeze is expected to hug the shore over northeast IL remaining east of ORD and MDW through the afternoon. Toward sunset, as winds diminish, the the lake breeze will probably make a run westward toward ORD/MDW. Best chance of a wind shift to easterly looks to be at MDW, but can't be ruled out at ORD.

If showers do develop near and over the lake this afternoon, outflow from the showers could provide the lake breeze an earlier westward push inland. Not out of the question this could threaten a temporary easterly wind shift at MDW and possibly even ORD later this afternoon.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement from late tonight through Sunday evening for ILZ103-ILZ104.

IN...Beach Hazards Statement from late tonight through Sunday evening for INZ001.

Beach Hazards Statement through Sunday evening for INZ002.

LM...Small Craft Advisory from 4 AM to 7 PM CDT Sunday for Wilmette Harbor to Calumet Harbor IL-Calumet Harbor to Gary IN.

Small Craft Advisory until 10 PM CDT Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.