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 /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 555 AM CDT Sat Aug 22 2026

Forecast concerns for the terminals...

- Breezy northwest winds today gusting around 20-25 kts.

- Low chance (15-20%) for an isolated shower or storm this afternoon.

Generally quiet weather conditions are expected at the terminals today in the wake of last night's cold front. Winds will gradually increase through the morning with gusts peaking around 20-25 kts this afternoon out of the northwest. Though, a lake breeze at GYY does look to result in a period of northeast winds after 20z there. While gusts are expected to ease after sunset, 6-8 kt winds will prevail overnight into Sunday before some 15-20 kt gusts return at the tail end of the TAF period. Otherwise, expect VFR conditions to prevail through the period with SCT to BKN 5000 ft ceilings near the lake. However, there are some MVFR ceilings developing over the lake early this morning that may result in a few hour window of MVFR conditions at GYY and maybe ORD and MDW through mid-morning.

Lastly, there is a low chance (15-20%) for an isolated shower or storm to develop near Lake Michigan this afternoon (mainly between 19z and 00z if they occur) as the shortwave trough over WI pivots through. Given the drying mid-levels suspect shower/storm coverage will be very spotty and therefore confidence on showers/storms actually reaching the Chicago area terminals is low. So for now have opted to forego a formal TAF mention, but will keep a close eye on trends.

Yack

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 from 10 AM CDT this morning 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 from 10 AM this morning to 10 PM CDT Sunday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.