textproduct: Chicago

KEY MESSAGES

- Periods of showers or sprinkles continue this afternoon. Additional showers and drizzle possible this evening and through the day on Monday.

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

- Warmer conditions on Tuesday expected to eventually trend slightly below average by next weekend.

DISCUSSION

Issued at 153 PM CST Sun Nov 1 2026

Broad mid-level troughing across the region, combined with numerous embedded perturbations and an expansive mid and upper- level cloud deck will continue to yield intermittent sprinkles or light showers across the area today. Guidance suggests there may be an additional flare up of light showers this evening associated with a modest increase in 295-300 K isentropic upglide. Later this evening and overnight, deep-layer moisture will shift east of the area as lower-level moisture surges out of central Illinois. As low stratus arrives, drizzle may develop and could persist through Monday morning. While an additional plume of moisture above 600 mb will arrive Monday afternoon, model soundings show a persistent dry wedge in place, and this may end up resulting in periods of drizzle just continuing intermittently through the rest of the day. Have cut high temperatures several degrees under NBM-delivered values (generally in the low 60s), and it's possible these may still be a few degrees too warm if cloud cover and drizzle remains persistent and widespread through the day. A tightening pressure gradient will result in a gradual increase in southeasterly breezes through the day.

On Monday evening and overnight, a robust shortwave will round the base of a long-wave upper trough and will eject out across the Texas/Oklahoma Panhandles. Strengthening southwesterly flow off the deck will lead to increasing warm advection which will maintain steady south to southeasterly breezes across the region through the night. Temperatures will likely hold steady or even slowly rise through the night. Most of the large scale forcing for ascent and attendant instability is forecast to remain west of the Mississippi River during this time. That said, a few waves of showers may develop and push across the region within the burgeoning warm advective regime.

The primary surface low is forecast to slowly progress across the Upper Mississippi Valley on Tuesday. As this takes place, initial sprockets of mid-level vorticity and associated height falls suggest large scale forcing will gradually increase across the area through the afternoon hours. This will likely result in an increase in shower and possibly some thunderstorm coverage, particularly west of the Fox Valley. The temperature forecast is a bit tricky as cloud cover looks to be expansive, but this will probably be offset to some degree by strengthening southerly winds, possibly gusting near 35 mph at times. Have trimmed highs a few degrees near and west of I-39, but felt NBM- delivered temperatures in the low to mid 70s farther east look appropriate at this point.

The most robust upper-level dynamics are forecast to arrive in our area Tuesday evening, during which time a notable uptick in NE/SW oriented 850-600 mb frontogenesis is progged to develop in the vicinity of the I-55/57 corridors. A period of steadier showers and a few embedded thunderstorms may develop in this corridor. The overlap of stronger jet forcing looks maybe just a bit too brief to raise a widespread heavy rainfall concern, although some localized corridors of enhanced precip amounts will certainly be possible wherever the main frontogenetic forcing develops, particularly if this ends up stalling and pivoting a bit more.

Showers may linger into Wednesday morning but coverage should tend to diminish with time. Low-level lapse rates will increase during the afternoon, and given the presence of the main upper- low still hanging around overhead, some renewed scattered shower development can't be ruled out. Gusty southwesterly winds (perhaps near 30-35 mph) will be possible on Wednesday.

Confidence in forecast details then decreases mid to late week, due to model differences in the further evolution of the slow- moving upper low across the region - complicated somewhat by the degree of phasing with a northern stream short wave across the upper Midwest/northern Lakes. Overall, the Wednesday night-Friday period continues to look at least intermittently unsettled as the closed upper low and occluded surface system track slowly east across the region, though some timing differences linger in the guidance at this distance. While no strong intrusion of colder air is evident at this time, temperatures do look to eventually cool to/slightly below average on the back side of this departing system.

Carlaw/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 Monday to 6 AM CST Wednesday for the IL nearshore waters.