textproduct: Chicago

KEY MESSAGES

- Cloudy with patchy drizzle or light showers today.

- Greatest chances for more widespread showers and perhaps a few thunderstorms late Tuesday afternoon and evening/early overnight.

- Windy and warmer conditions on Tuesday. Temperatures then expected to trend slightly below average by the weekend.

DISCUSSION

Issued at 252 AM CST Mon Nov 2 2026

Early morning GOES water vapor imagery depicts a long-wave upper trough across the western CONUS. Weak mid-level ridging was noted downstream into the Mississippi Valley and western Great Lakes region. Latest surface map does indicate widespread low stratus just off to the south of the CWA across central IL/IN however, and this low-level moisture is expected to spread north across the forecast area this morning as low level south- southeast flow begins to strengthen downstream of the western trough. Have noted some minor (4-7SM) drops in visibility and some very weak clear-air VCP returns beneath stratus downstate, suggesting some patchy drizzle may be occurring, and this may spread north across our area this morning. Have continued to undercut NBM temperature guidance for today by roughly 3-5 degrees (low-mid 60s) even with southeast winds becoming breezy, given the expected extensive low-cloud cover. Model forecast soundings and time/height sections do indicate some increase in mid-level moisture later today with an approaching low-amplitude short wave currently over IA/MO, especially over northwest IL, where some scattered showers appear possible later this afternoon.

Tonight, a strong mid-level short wave currently heading into the central/southern Rockies is forecast to wrap northeastward across the Plains. Guidance remains in good agreement in depicting the development of a 45-50 kt low-level jet into the Midwest ahead of this feature, which will result in maintaining southerly surface winds that will likely result in steady or slowly rising temperatures overnight. The strongest forcing/ascent continues to focus west of the Mississippi River overnight, though persistent warm advection/isentropic ascent is forecast to produce bands of showers from IA, across northwest IL into WI, mainly across the northwest third or so of the CWA.

Surface low pressure currently over far northeastern CO is forecast to lift northeast across eastern SD today and into MN this evening. A second area of low pressure associated with the strong Plains short wave is forecast to develop into the Kansas City vicinity by Tuesday morning, and eventually consolidate across MN/western WI by early Wednesday. During the course of this evolution, large scale forcing will gradually increase and result in increasing shower and possibly some thunderstorm coverage from west to east across the Illinois portion of the forecast area by Tuesday afternoon, especially west of the Fox Valley. Strong southerly winds, potentially gusting around 35 mph at times, will work to boost temperatures across the area. Greater rain/shower coverage across our western CWA may limit warmth somewhat there, though low-mid 70s continue to look reasonable for afternoon highs farther east. Tuesday evening/overnight continue to be the focus for the strongest large-scale forcing, including mid-level height falls, and increasing low/mid-level baroclinicity, and frontogenetic forcing ahead of the system's occluding cold front. Guidance continues to depict that an axis of heavier QPF in the vicinity of the I-55/I-57 corridors may develop Tuesday night in association with a SSW-NNE oriented region of mid-level frontogenesis. This may support a period of steadier rain/embedded thunderstorms which could produce a localized corridor of heavier rainfall amounts. The occluding cold front is forecast to move across the area Wednesday morning, with shower coverage decreasing and becoming more scattered behind the front. Temperatures will be cooler Wednesday, though still above average for early November with expected highs in the low- mid 60s. Southwest winds will likely remain gusty, potentially still 30-35 mph.

Models continue to show some spread by the end of the week with how quickly the system departs, with the GEFS faster and the CMCE slowest. Eventually however, weak surface high pressure is expected to develop by late Friday/Saturday, with a cool-down to slightly below average temperatures (50s by day, 30s at night). There is a signal in all of the global guidance for another northwest-flow short wave to dig into the western Lakes region toward Sunday, which may support additional shower chances.

Ratzer

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1201 PM CST Mon Nov 2 2026

Key messages for the 18Z TAF period:

* MVFR cigs through Tuesday with periods of IFR

* Pockets of drizzle possible overnight into Tuesday with showers expected during the afternoon

* Gusty southerly winds, especially on Tuesday

Low MVFR cigs are parked over Chicagoland early this afternoon with IFR found farther inland, including over RFD. RFD is expected to lift to MVFR late in the afternoon. MVFR cigs are then anticipated through the daytime on Tuesday with periods of IFR possible.

A weak signal exists for a brief push of drizzle and IFR cigs across Chicagoland late this afternoon. Chances in these impacts materializing are too low to include in the TAFs. A better signal exists overnight into early Tuesday. A system of true rain showers will then move in from the west during the day. Rain could reach RFD as early as mid-morning and Chicago by early afternoon, but chances are highest later into the afternoon.

Meanwhile, southerly winds at around 10 to 12 kt sustained will continue to gust as high as 20 kt through the afternoon and into the 20 to 25 kt range for much of the evening and overnight. Tuesday late morning and afternoon are expected to see regular gusts out of the south to 30 to 35 kt.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 6 PM this evening to 6 AM CST Wednesday for the IL nearshore waters.

Small Craft Advisory from 9 AM Tuesday to 6 AM CST Wednesday for the IN nearshore waters.