textproduct: Chicago

KEY MESSAGES

- Periods of rain/showers will continue through tonight across much of the area, and through Friday night for portions of northwest IN downwind of Lake Michigan.

- Breezy and cooler conditions expected Friday.

- Freezing temperatures likely for much of the area Friday night, and possible again Saturday night and Sunday night in some locations.

- Dry and warmer than average weather early next week.

DISCUSSION

Issued at 248 AM CST Thu Nov 5 2026

00Z upper air analysis and current GOES water vapor imagery depicts an upper level trough across the upper Mississippi Valley and western Great Lakes region. Embedded within the trough was a closed low over northern WI and the UP of MI, as well as a couple of decent vorts (one notably over eastern IA), wrapping cyclonically southeastward through the base of the trough. This pattern will continue to support periods of light rain/showers and drizzle especially north of the I-80 corridor this morning. The main upper trough axis is progged to develop southeastward this afternoon, while surface low pressure currently analyzed over eastern Lake Superior moves east and trails a secondary, fairly-stout cold front across our forecast area this afternoon and evening. An increase in shower coverage is expected as this occurs, along with a shift to blustery northerly winds and colder temperatures behind the front into tonight. The bulk of the rain/showers should gradually end from northwest to southeast across the CWA overnight, though strong cold advection down the fetch of Lake Michigan (H8 temps as low as -4/5C by early Friday) will set up conditions conducive (delta-T 15-19C, ELs near 9 kft) for lake-effect rain showers into northwest IN from later tonight through Friday/Friday night.

Blustery north-northwest winds maintain low-level cold advection across the area Friday, though winds should gradually ease late in the day/evening. Temperatures look to be limited largely to the upper 40s across much of the area, perhaps tagging 50 if clouds break up enough by afternoon over northern IL. Surface high pressure then builds into the region later Friday night into Saturday morning, with clearing skies and diminishing winds expected to allow for freezing overnight lows in the upper 20s/lower 30s across much of the area except the core of the Chicago urban center and northwest IN where clouds/warmer temps are expected downwind of the lake. No frost/freeze headlines are planned, as we're now well past the climatological first freeze date this fall. Dry but cool conditions are expected Saturday with the surface ridge continuing to drift southeast across the area, with highs around 50 and lows again Saturday night around 30 away from the city.

Ensembles are in good agreement in maintaining dry weather from this weekend through early next week, with the jet stream focused just to the north of the region, and an expansive area of surface high pressure from TX to the southern Appalachians/mid-Atlantic region blocking any Gulf moisture return. Models do indicate a Pacific cold frontal passage in the Monday night/early Tuesday timeframe, though with no precipitation forecast. Temperatures are expected to run at or above average (especially daytime temps) with highs in the upper 50s/low 60s (Monday looks warmest ahead of the Pacific front) and lows in the 30s/40s.

Ratzer

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 558 AM CST Thu Nov 5 2026

Main Concerns:

- Wind shift to gusty northerly early this evening may include a brief north-northeast direction at ORD and MDW

- Primarily MVFR CIGs through tonight, with periodic IFR

- Showers mixed with drizzle will result in MVFR VSBY at times, particularly this afternoon and evening

Precip and Flight Categories: While MVFR CIGs are indicated in the TAFs to start the period, there will be periods of VFR this morning. -SHRA/-DZ appear likely to be much more sporadic until this afternoon with the approach of a cold front. When shower and drizzle activity fills back in this afternoon, IFR CIGs will also become more prevalent, at least on a temporary basis. -SHRADZ will focus closer to Lake Michigan this evening, resulting in at least occasional MVFR VSBY at the Chicago metro terminals. MVFR CIGs should scatter out sometime overnight into Friday morning.

Winds: Occasionally gusty west-southwest winds will veer to west-northwest this afternoon, and then quickly northerly/north- northwest (gusts to ~20-25 kt) with the cold frontal passage early this evening. Confidence is medium in the exact timing of the wind shift. It's possible that the wind shift arrives during the back half of the 00z hour at ORD. Indicated temporary 010 deg direction at ORD and MDW this evening, and can't rule out a short period of 020 to 030 deg directions. Breezy north-northwest winds (330-3500 deg will continue through the day on Friday.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 9 AM CST this morning for the IL and IN nearshore waters.

Small Craft Advisory from 6 PM this evening to 9 AM CST Saturday for the IL nearshore waters.

Small Craft Advisory from 6 PM this evening to 3 PM CST Saturday for the IN nearshore waters.