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 /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1156 AM CST Sun Nov 1 2026

Spotty light SHRA from a mid-level cloud layer will continue into early afternoon, followed by perhaps a couple instances of sprinkles into mid-evening. Otherwise, VFR conditions will persist through at least the early morning hours as winds under 10 knots favor directions in the SE quadrant. Winds will then settle SSW/S while increasing to over 10 knots for much of the day Monday.

As mid-level moisture exits the area to the northeast overnight, low-level moisture will gradually advect northward across Illinois. Low-level MVFR ceilings are expected to shift over the Chicago terminals within an hour or two on either side of sunrise Monday. Ceilings may lower into IFR levels during the morning and early afternoon, with cloud depths also becoming sufficiently deep for DZ. Confidence was low enough to limit the mention of lower conditions to a PROB30 at the Chicago terminals. IFR ceiling and DZ potential will increase with westward extent, so have prevailed lower conditions at RFD during most of the morning.

Kluber

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.