textproduct: Chicago

KEY MESSAGES

- Scattered showers and a few embedded thunderstorms tomorrow.

- Unseasonable warmth on Saturday followed by a period of showers Saturday night and Sunday morning mainly near and southeast of I-55.

DISCUSSION

Issued at 220 PM CDT Thu Oct 8 2026

It's been another pleasant early October day out there today with temperatures early this afternoon in the lower and middle 70s and only a few passing high level clouds overhead. Conditions will remain quiet through the night as temperatures drop into the upper 40s and lower 50s by early Friday.

A prominent center of high pressure is parked over the Ozark Plateau this afternoon and we find a region of warm advection developing over the north-central Plains as the high helps to pump mild southerly flow into the region. This warm advective wing will focus into Iowa this evening. Deep isentropic ascent and a corridor of frontogenetic forcing will foster an area of precip to our west tonight. This feature will sharpen as it gets shunted east across northern IL tomorrow morning into afternoon. Scattered showers are expected in our area for much of the daytime beginning as early as predawn near and west of I-39. Highest coverage through the day is generally favored near and north of the Kankakee River valley along a theta-e gradient that looks to develop on the northern periphery of the warm advective push, although rain will be possible anywhere around the area. Have boosted PoPs in the forecast and expanded to now bring at least slight chances to the whole area through the day.

As the low levels continue to warm, mid level lapse rates will steepen through the day such that some embedded elevated thunderstorms will also be possible, especially after mid- morning. There remains some uncertainty in how much instability can build atop the area. The main pool of instability will remain west of the Mississippi while models generally top out below 1,000 Joules of elevated CAPE across northern IL by the afternoon. The general lack of instability should hinder a strong storm threat, but 30 to 40 kt of effective shear may allow some cores to organize. Coverage should mostly exit the CWA by the end of the afternoon. Modeled QPF is largely on the order of one to two tenths or less, but many camps, especially the convective-allowing camps, suggest more noteworthy amounts are possible on an isolated basis with the potential for pockets of heavier rain and thunderstorms.

There's quite a bit of spread in temperature guidance tomorrow with uncertainty in the exact northward extent of the warm advection. Most of the area is favored in the 70s but could be stuck in the 60s near and north of I-80. Saturday should be much warmer with highs progged in the lower 80s area-wide and mostly sunny skies into the afternoon. Cloud cover looks to build later in the day as the remnants of Hurricane Isaias work their way up into the region.

The core of the storm will stay to our south and southeast as it tracks across the Tennessee and Ohio valleys, but it's still unclear how far northwest layer moisture will stretch that can support precip Saturday night into Sunday. These remnants will be clashing with a notably dry airmass over the Midwest and the better synoptic forcing will also focus to our south and east. In the forecast, maintained slight chance PoPs as far northwest as the I-55 corridor during the overnight and morning periods with low-end chances east of I-57 and into northwest IN.

Additional opportunities for rain are in the forecast next week including along a cold front Monday-night into Tuesday and with another large synoptic system favored to traverse the region in the Wednesday to Thursday window. Prior to that cold front, Monday will be another unseasonably warm day with highs progged in the upper 70s and lower 80s. More seasonable temperatures are then favored into late week.

Doom

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 609 PM CDT Thu Oct 8 2026

Key Aviation Messages for the current TAF period:

- Showers and a chance for thunderstorms late Friday morning through the afternoon

A weak lake breeze is currently passing through the Chicago terminals. Both the northwest winds west of the lake breeze and northeast winds on the east side have generally been light and less than 8 knots. This lake breeze is expected to wash out after 00Z as the sun sets with light and variable winds expected overnight.

Winds are expected to be out of the southeast through most of Friday. Models remain in fairly good agreement with scattered showers moving in mid morning around KRFD and late morning for the Chicago terminals, and remaining through most of the afternoon. Confidence is lower on the exact coverage of any embedded thunder as models are showing a weakening trend in the instability as it moves through. That being said, there should be enough instability to keep the chance for thunder in the TAFs and make no changes to the PROB30 at this time. Drier conditions are expected after 00Z as the rain exits to the east-northeast. Winds will diminish and become more southerly during the evening (if not flop over to the southwest toward 06Z).

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.