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 /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1127 PM CST Sun Nov 1 2026

Forecast concerns include...

Low MVFR CIGs, possible IFR CIGs, Monday/Monday night. Chance of showers/drizzle Monday. Gusty south/southeast winds Monday/Monday night.

The leading edge of MVFR CIGs is steadily lifting north across central IL late this evening and should spread across the terminals in the predawn hours. Low MVFR CIGs are then expected to continue through at least daybreak Tuesday morning. IFR CIGs will be possible at times, though confidence is low. There may be a short period of IFR CIGs Monday morning, associated with patchy drizzle. Both remain handled well with PROB mention. If IFR cigs were to become prevailing, the favored areas would be across northwest IL. IFR CIGs are then possible again Monday evening into early Tuesday morning, again more favored across northwest IL. In addition to the drizzle potential Monday morning, isolated showers are possible through the period. There may be a better chance for showers across northwest IL and for RFD Monday afternoon into Monday evening, and opted to include vicinity mention for this potential.

Southeast winds will remain generally under 10 kts through the predawn hours and then begin to increase to 10-12 kts by/around sunrise. Gusts to 20kts will develop by late morning/early afternoon and continue into Monday evening. Directions will turn more southerly Monday evening, with gusts increasing into the lower/mid 20 kt range. cms

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.