textproduct: Chicago

KEY MESSAGES

- A fall storm system will move through the area Thursday and Friday, bringing periods of rain showers and gusty northwesterly winds (the latter primarily on Friday).

- Frosty and near-freezing conditions are favored away from Lake Michigan Friday night into Saturday.

- After the brief period of chilly weather, there will be a warming trend this weekend into early next week.

DISCUSSION

Issued at 310 PM CDT Wed Oct 14 2026

Through Thursday night:

Other than a few spits of drizzle near Lake Michigan, most of the area has since dried out from the overnight and early morning showers and thunderstorms. The combination of overcast skies and persistent onshore northeasterly winds have held temperatures in the low to mid 60s near/north of I-80. Farther south, a thinning of the stratus layer with occasional peeks of sunshine has allowed temperatures to warm into the upper 60s and lower 70s. Generally expect the cloud cover to fill back in through this evening and overnight with temperatures only dropping into the 50s.

A fall storm system remains on track to lift across the region on Thursday which will bring widespread showers and a few rumbles of thunder to the area. The greatest shower coverage is currently favored late morning through the afternoon. Hi-res guidance continues to depict a relative minimum in precipitation developing on the southwest side of the surface low during the late afternoon and early evening. Depending on how far north the low tracks, increasing instability southeast of this dry wedge may lift into the far southern forecast area, south of a Pontiac to Rensselaer line. While the better instability remains farther south into central and southern Illinois, an isolated stronger storm can't be ruled out. Any more robust showers and embedded thunderstorms will be capable of efficient rainfall rates for this time of year in the presence of PWATs potentially upwards of 1.5-2". The limited coverage of stronger showers/storms should keep any flooding potential tied mainly to ponding on roadways and poor drainage spots.

Friday:

In the wake of the departing storm system and associated strong cold front, the surface pressure gradient increases markedly across the area on Friday. This will lead to blustery northwest winds gusting up to 30-40+ mph, highest along the northwest Indiana lakeshore. In addition, model guidance has trended slightly more saturated within the low-cloud layer which may support the redevelopment of gusty diurnal showers. Weak instability within the layer and colder cloud tops may support some graupel as well. Temperatures on Friday will likely struggle to warm out of the low to mid 50s, making for the coldest day of the season so far.

As the northwesterly winds begin to turn more northerly over Lake Michigan, a broken band (or bands) of lake effect rain showers will focus into northwest Indiana late Friday afternoon through the evening. Waves are also expected to increase and may lead to minor lakeshore flooding or erosion, particularly along the Porter County shore.

Friday night onward:

Skies will quickly clear out after midnight Friday, which will allow for efficient radiational cooling amidst an already cooler airmass. This will likely lead to areas of frost development outside of Chicago and away from Lake Michigan, coverage dependent upon how light winds end up. Can't rule out temperatures in portions of interior northern Illinois dropping into the lower 30s. However, confidence is not high enough for a freeze watch with this update.

While still cooler on Saturday with temperatures in the 50s to around 60, a return of southwesterly low-level flow will begin a gradual warming trend that continues through early next week, bringing a return to above normal temperatures.

Petr

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/

Issued at 658 PM CDT Wed Oct 14 2026

Key aviation forecast messages:

- Patchy MVFR ceilings this evening/overnight.

- Rain develops early Thursday morning, with conditions deteriorating through low-MVFR into IFR by late morning/midday.

- Period of LIFR ceilings possible later afternoon/early evening especially for Chicago terminals.

Early evening surface analysis places a nearly stationary frontal boundary across the lower Ohio Valley, while high pressure was centered over the northern Great Lakes. Northeast winds along the southern periphery of the high, combined with some lingering low-level moisture has maintained some patchy MVFR ceilings across parts of northeast IL and southeast WI. Guidance trends had indicated scattering of the lower clouds this evening, though recent obs trends near Lake Michigan lend low confidence in these trends this evening.

Later tonight into early Thursday, surface low pressure is expected to deepen across the Plains in response to a strong upper level trough. Guidance is in good acquirement that this progression will lead to an expansion of rain/showers into the region early Thursday morning, with a corresponding gradual deterioration of ceilings into MVFR early and to IFR by late morning/midday, with winds becoming east-southeast to southeast through the day. There is some model support for a period of LIFR ceilings and IFR vis later in the afternoon/early evening, especially across the Chicago terminals, as the surface low and associated frontal zone lift into the area.

As the surface low tracks east of the area Thursday evening, winds will shift to the northwest and begin to increase toward the end of the current TAF period. Winds will likely become lighter and somewhat variable in the vicinity of the surface low with IFR/LIFR conditions likely early before the increasing northwest winds allow for some gradual improvement back to MVFR overnight.

Ratzer

MARINE

Issued at 310 PM CDT Wed Oct 14 2026

Strong northwesterly gales to 40 kt and very hazardous waves are forecast to develop Friday afternoon in the wake of a departing fall storm system, becoming more northerly into Friday evening. Accordingly, a Gale Watch has been issued for the Illinois and northwest Indiana nearshore waters from 1 PM Friday through 1 AM Saturday.

Increasing lake induced instability will become supportive of the development of a band of lake effect showers over Lake Michigan Friday afternoon and evening. Waterspouts also cannot be ruled out within the strongest showers.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CDT Thursday for Winthrop Harbor to Wilmette Harbor IL.

Gale Watch from Friday afternoon through late Friday night for the IL and IN nearshore waters.

Small Craft Advisory until 10 AM CDT Thursday for Wilmette Harbor to Northerly Is. IL.

Small Craft Advisory until 4 AM CDT Thursday for Northerly Is. IL to Michigan City IN.