textproduct: Chicago

KEY MESSAGES

- The potential for showers and potentially strong to severe thunderstorms returns Wednesday afternoon and evening along a cold front.

DISCUSSION

Issued at 207 PM CDT Mon Aug 24 2026

High pressure centered over the area this afternoon will drift southeastward through Tuesday, supporting a dry and relatively quite period of weather. Patchy shallow fog will be possible late tonight primarily for interior areas south of the Chicago metro and across northwest Indiana. Otherwise, expect another cool night tonight with lows in the 50s and mild day Tuesday with highs around 80.

An upper-level low centered just north of the Boundary Waters of Minnesota Tuesday night will track to east of Lake Superior by Wednesday evening. A series of weak mid-level impulses will pinwheel around the low across Wisconsin and Lower Michigan during this time. Meanwhile, mid-level moisture originating from the southwestern CONUS will advect northeast across the mid- Mississippi River Valley as modestly steeper mid to upper-level lapse rates shift over the area. Conditions appear favorable for at least some convection over the forecast area during the afternoon and early evening, but there are several factors that complicate both the coverage and severity of that convection. The initial weak waves late Tuesday night through early afternoon Wednesday will bring mid-level clouds and possibly decaying high-based showers and embedded thunderstorms, resulting in questions with sufficient destabilization even as a narrow ribbon of higher low-level moisture advects in from the southwest. Forcing may also remain mis-aligned, with the upper- low to the north, tail-end of the mid-level troughs overhead, relatively weak upper-level jet to the south, and trailing cold front to the west. Conditional on erosion of the low-level cap and better alignment of the forcing noted above, deep-layer shear will be favorable for multicell clusters with embedded weak supercell structures, with locally damaging winds the primary threat, mid-afternoon into early evening.

Mid-level ridging over the Canadian Prairies will deamplify while shifting eastward late this week into the weekend. Associated surface high pressure will track east while becoming elongated across the central Great Lakes Thursday and Friday. Cannot fully rule out sprinkles or weak showers on the lake breeze boundary across northeast Illinois late Thursday afternoon, but the subsidence inversion should be strong enough to stunt any growing diurnal cumulus.

A loosely zonal pattern across North America this weekend into early next week favors a more active storm track north of the forecast area, but close enough to warrant periods of low-end precip chances for showers and some thunderstorms as early as Saturday night. Summer warmth will also return as we close out August with increasing humidity and daytime highs pushing well into the 80s (assuming active weather remains bottled up to the north).

Kluber

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 626 PM CDT Mon Aug 24 2026

Key Aviation Messages for the current TAF period:

- Potential for MIFG at terminals way from the city of Chicago

No significant weather is expected through the TAF period. A lake breeze has switched winds at terminals closer to lake Michigan to the east, though remaining 10 knots or less. Winds at terminals west of the lake breeze remain northwesterly, but all winds will gradually diminish and become light overnight. Winds will become southwesterly tomorrow morning, but remain 10 knots or less through the day. Models are suggesting another weak lake breeze could develop tomorrow afternoon near the shoreline, but not expected to move west toward ORD/MDW.

There is a low chance for localized MIFG and/or BCFG at rural terminals overnight that may reduce vis slightly (5-6 SM), but confidence is low.

DK

LOT WATCHES/WARNINGS/ADVISORIES

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