textproduct: Chicago

KEY MESSAGES

- Breezy and seasonably chilly conditions persist this afternoon with some scattered showers.

- East of Gary, lake enhanced showers this afternoon will transition to lake effect showers tonight with a slight chance of a thunderstorm near the shore late this afternoon/early this evening. Wind gusts to 45 mph possible near the northwest Indiana lakefront this afternoon/early evening.

- Coldest night of the season expected tonight with lows near/just below freezing across interior portions of northern IL.

- Dry and mild weather returns Sunday and persists next week.

DISCUSSION

Issued at 133 PM CDT Fri Oct 16 2026

A seasonably strong and expansive high-pressure system over the Great Plains continues to build eastward into the Midwest this afternoon, following a surface low moving into New England. Strong northerly winds between these systems are pushing the season's coldest airmass southward into the area, resulting in a cloudy, chilly, and breezy day across the region. A few widely scattered showers remain possible across northern Illinois through sunset as an upper-level trough moves overhead. However, shower activity will primarily concentrate over Lake Michigan late this afternoon and evening as lake-effect parameters rapidly improve. This should lead to focused lake-effect showersand potentially a few thunderstormsshifting inland from southern Lake Michigan into northwestern Indiana this evening. Scattered lake effect showers may linger after midnight, but they are expected to diminish toward Saturday morning as inversion heights lower and lake-effect parameters weaken following the passage of the upper-level trough.

Outside of lake-effect precipitation and cloud cover in northwestern Indiana, skies will clear and winds will gradually subside this evening. This will be especially true across interior portions of northern Illinois, where the coldest temperatures of the season are forecast tonight. The current forecast remains on track for a couple of hours of near-freezing temperatures early Saturday morning, most notably across far northern Illinois from the Fox Valley westward. Consequently, no changes were made to the frost and freeze headlines in effect for interior northern Illinois late tonight.

Following a chilly and frosty start on Saturday, full sunshine and light winds are forecast as the surface high moves directly over the region. The abundant sunshine will help temperatures rebound into the upper 50s during the afternoon. Another chilly night will follow Saturday night as temperatures drop back into the 30s. Given the light winds, additional frosty conditions are possible, particularly east of I-55 where the lightest winds are expected. We will continue to monitor this period for potential frost headlines.

The cold snap will be short-lived as conditions transition back to a mild and dry autumn pattern. High temperatures are forecast to return to the 60s on Sunday and Monday, before warming into the 70s for the remainder of next week with little to no chance of rain.

KJB

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1234 PM CDT Fri Oct 16 2026

Key concerns for the 18Z TAF period:

* Scattered light showers this afternoon

* MVFR cigs over Chicagoland returning to VFR this afternoon

* At GYY, periods of lake-effect rain expected late this afternoon and again late tonight into early Saturday

Scattered coverage of light rain is dropping into northern IL from the north early this afternoon. Periods of light rain will be possible through the rest of the afternoon. MVFR cigs over the region have recently scattered out over RFD with more VFR found upstream. Chicagoland sites are expected to return to VFR by mid- afternoon.

At GYY, a band of lake-effect rain showers will target far northwest IN late this afternoon into early evening. Periods of light to moderate rain with MVFR vsby reductions are anticipated. A second push is expected after midnight and may last into early Saturday.

Meanwhile, NW winds will trend toward NNW through the afternoon while regular gusts are expected to get up to near 30 kt for the middle and late afternoon. NNW winds will remain gusty through much of the night before easing for Saturday.

Doom

MARINE

Issued at 133 PM CDT Fri Oct 16 2026

Northerly gales to 40kt are forecast this afternoon and evening, with strongest gusts to 40kt+ likely within the lake enhanced convergence band and with more robust lake effect showers over the Indiana waters east of Gary. In addition to an isolated thunderstorm or two late this afternoon, conditions are expected to become favorable for waterspouts late this afternoon into this evening. Waterspout risk is expected to diminish late this evening as inversion heights lower. Lake effect shower intensity and coverage will decrease overnight also in response to the decreasing inversion heights.

LOT WATCHES/WARNINGS/ADVISORIES

IL...Freeze Warning from 5 AM to 8 AM CDT Saturday for ILZ003- ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012.

Frost Advisory from 5 AM to 8 AM CDT Saturday for ILZ006- ILZ019-ILZ020.

IN...Wind Advisory until 10 PM CDT this evening for INZ002.

LM...Gale Warning until 1 AM CDT Saturday for the IL and IN nearshore waters.