textproduct: Chicago

KEY MESSAGES

- Below average temperatures are expected through the weekend before temperatures turn more seasonable early next week.

- No significant widespread precipitation chances are expected at this time until the middle of next week.

DISCUSSION

Issued at 105 PM CDT Thu Sep 24 2026

The forecast area remains on the northwestern periphery of an upper-level low which is progged to deepen across the mid- Atlantic region over the next couple of days. Various model guidance indicates the potential for some spotty showers to spread into far north/northwest IL toward daybreak Friday, in association with an short wave propagating into the upper Midwest. This wave will be running into short wave ridging aloft on the northwestern fringe of the deepening east coast low however, which along with easterly low-level dry air advection is expected to limit the eastward development of precipitation. Have maintained some slight chance (<=20%) pops for these decaying showers mainly west of the Fox River Valley across northern and northwest IL between about 4AM-10AM Friday morning.

Behind Friday's wave, the narrow upper-level ridge is then progged to briefly redevelop into the upper-Midwest Friday night into Saturday before another short wave approaches the upper- Midwest Saturday evening. Similar to Friday morning's scenario, this wave will also be fighting the ridge and dry easterly low- level flow. Some decaying showers will again be possible Saturday night across our far western counties of the forecast area, but did not include a formal mention in the outgoing forecast. Partly to mostly cloudy skies and continued modest east-northeast surface winds will likely keep our temperatures slightly below average in the mid-60s to lower 70s both Saturday and Sunday.

A slower evolution is not unusual in such highly-amplified upper air patterns, and the latest global model/ensemble solutions have delayed kicking out the eastern low until early- mid next week. As this occurs, there are indications that the pattern will become more active with an eastward-moving frontal zone and surface low developing into the region toward mid- week. NBM initialization depicts this with 40-60% pops later Tuesday into Wednesday and made no changes at this distance, though there is quite a bit of ensemble spread in the current EPS/GEFS/CMCE solutions with the timing/strength and placement of features at this time.

Ratzer/Borchardt

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 653 PM CDT Thu Sep 24 2026

The area will remain on the southwest periphery of a slow- moving high pressure through the period. Winds will remain between NE and ESE around 10 knots or less.

Patches of high-end MVFR to low-end VFR stratus will filter over the terminals into the overnight hours. Otherwise, VFR conditions are expected through the period with a less than 20 percent chance for a few sprinkles very late tonight into Friday morning.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

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