textproduct: Chicago

KEY MESSAGES

- Periods of scattered showers are expected at times into Friday, most notably Thursday and Thursday night.

- Breezy and cooler weather is expected through Friday.

- Potential for freezing temperatures across portions of the area Friday and Saturday nights.

DISCUSSION

Issued at 256 AM CST Wed Nov 4 2026

Surface low pressure was analyzed just southeast of KMSP as of 1 AM CST, with a trailing cold front extending to its south, just west of the Mississippi River over far eastern IA/MO. Aloft, GOES water vapor imagery depicted a strong negative-tilt short wave lifting northeast across MO toward western IL. Strong forcing ahead of this wave, combined with moisture advection on enhanced 45-50 kt 850-500 mb south-southwesterly flow, continues to produce an area of rain from the lower Ohio Valley northwest across the region. This area of rain will continue to shift to the north-northeast, with the trailing edge of the more organized precipitation along the I-39 corridor eventually moving east of the forecast area this morning. Though drier mid- level air will spread across the area, lingering low-level moisture will likely continue to support the potential for some patchy light rain or drizzle at times through the day. Strong south winds sporadically gusting 25-30+ mph ahead of the cold front overnight have held temperatures in the 60s overnight, though as winds shift southwest and ease a bit with the cold frontal passage today, temperatures will gradually fall into the 50s. Lingering cloud cover and breezy southwest winds tonight will keep temperatures in the 45-50 degree range.

The surface low to our north will only slowly drift northeast across the northern Great Lakes this afternoon into Thursday, as it occludes and becomes stacked beneath a slow-moving upper low/trough. This upper trough will be slow to move east over the next couple of days, as a series of smaller-amplitude short waves rotate about. This will maintain the potential for periods of scattered showers across the area at times, most notably Thursday into Thursday night, as a secondary cold front pushes southeast across the area. Highs in the 50s are expected again Thursday, with temperatures dropping into the upper 30s/low 40s Thursday night in breezy north flow behind the cold front.

Guidance is in decent agreement in digging a short wave southward into the upper trough over the Great Lakes region Thursday night, and developing a new closed upper-level low over lower MI by early Friday. This looks to reinforce low-level cold advection across the western Great Lakes region, setting up lake-effect showers over Lake Michigan and northwest IN Friday into Friday night, before the upper trough axis shifts east/southeast, and eventually lowers inversion heights over the lake. Model ensembles then indicate surface high pressure builds south across the upper Midwest and Mississippi Valley Friday night into Saturday. Decreasing cloud cover and diminishing winds associated with the surface ridge, combined with sub-zero H8 temps may set the stage for freezing conditions especially across the IL portion of our CWA late Friday night/early Saturday morning. Confidence is lower in a freeze over northwest IN, downstream of the warmer lake and potentially with some lingering lake-effect clouds. Dry weather is then expected Saturday/Sunday as the surface continues to drift southeast. Near average temperatures are forecast (highs in the 50s, lows mainly in the 30s). Ensembles suggest upper ridging develops into the region early next week, with temperatures potentially trending slightly above average again Monday- Tuesday.

Ratzer

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 604 AM CST Wed Nov 4 2026

Main Concerns:

- Lower CIGs most of the period

- Showers and/or drizzle at times

Aside from a brief VFR interval this morning, primarily MVFR CIGs are expected the rest of the period. Upstream obs of patchy higher IFR CIGs suggest those may occur at times as well. A few more waves of light showers and drizzle could temporarily knock VSBY down to MVFR. Confidence is low on specifics with additional rounds of -SHRADZ, and highlighted first potential window with a PROB30 (late this morning through early to mid afternoon). It appears RFD area has the best chance for showers and/or drizzle to linger into tonight, though it can't be ruled out farther east as well.

Winds will shift from breezy southerly/south-southwest as of this writing to southwesterly (220-240 deg) with a cold front passage later this morning. Gusts will regularly be into the 20-25 kt range.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST Thursday for the IL and IN nearshore waters.