textproduct: Chicago

KEY MESSAGES

- Period of rain showers Sunday morning, followed by mostly dry conditions for the afternoon.

- Additional period of showers and thunderstorms (30-50% chance) late Monday into Tuesday. A few storms could become strong to severe (mainly south of I-80) Monday evening.

- Outside of a brief warmup Sunday into Monday, near to below normal temperatures are favored through next weekend with occasional chances for rain showers.

DISCUSSION

Issued at 209 PM CDT Sat May 2 2026

Subtle mid-level ridging continues to reside across the Midwest and western Great Lakes this afternoon which will keep tranquil weather conditions in play through tonight. Despite the widespread diurnal cumulus, temperatures have continued to warm into the lower to mid- 50s and there is a chance that some locations could even attempt to tag 60 (mainly near and west of I-39) before sunset. As the diurnal cumulus erode this evening, temperatures should cool into the upper 30s to lower 40s before additional cloud cover returns after midnight. Given the increasing cloud cover overnight and the slightly elevated winds, conditions do not look overly favorable for widespread frost tonight. However, some localized pockets of patchy frost may still develop especially across northwest IN.

Heading into Sunday, the shortwave trough that is currently near the ND-Canadian border will be pivoting into northern IL. As it does so it will be interacting with a plume of mid-level moisture which should lead to the development of scattered showers across northern IL and eventually northwest IN. Since the wave is expected to be rather progressive, the rain showers should only last 2-3 hours at any one location and should fully exit our forecast area by early afternoon. In the wake of the shortwave, modest subsidence and a plume of drier air aloft should keep the atmosphere capped to any additional shower development Sunday afternoon. However, there will be a weak surface convergence boundary stretching from northeast OH to eastern MO Sunday afternoon which may allow for some isolated showers or storms to develop near this boundary and drift into our far southern CWA during the late afternoon and evening hours. With the aforementioned capping and the boundary forecast to be south of our area have opted to keep some silent (10-14%) POPs near and south of US-24 just in case but suspect we should stay dry.

Otherwise, Sunday will feature more typical early May temperatures in the mid to upper 60s courtesy of stout southwesterly winds. That said, expect wind gusts Sunday afternoon to peak around 30-35 mph despite the partly to mostly cloudy skies. Gusts will taper Sunday evening as skies clear and the atmosphere decouples. Though the continued warm advection will keep temperatures mild in the mid-40s.

A secondary and more amplified shortwave trough will be digging out of Canada towards the Great Lakes on Monday which in turn will push a cold front southward towards and eventually through northern IL and northwest IN. Guidance has come into better agreement that the cold front should remain north of our area until late Monday afternoon and evening which means that most of the daytime hours should be dry. Additionally, the prevailing southwesterly breezes look to allow temperatures to top out in the mid-70s Monday afternoon. Though, once the cold front arrives it will bring with it widespread showers and thunderstorms. Forecast soundings ahead of the front continue to show that low-level moisture may be limiting factor (dew points forecast to be in the lower to mid-50s) which could limit the coverage of thunderstorms especially for the northern half of our area. That said, there will be sufficient instability to at least support some storms Monday afternoon and evening and given that there will be around 35-40 kts of deep layer shear present, a few storms could even become strong to severe. While the Storm Prediction Center does have a marginal (level 1 of 5) risk for severe storms Monday evening for areas south of I-80, the aforementioned limited moisture does make this threat low confidence. Regardless, if any strong to severe storms do materialize the main threats look to be gusty winds and instances of hail.

The cold front and its associated showers will progress into central IL and IN Monday night into Tuesday, but will begin to stall as it does so. This stalling boundary in addition to the continued forcing from the shortwave trough over the Midwest (that may even attempt to phase with a southern CA shortwave) should keep showers and isolated storms ongoing through much of the day on Tuesday. With the better instability expected to be south of our area into central IL and IN the threat for severe weather looks very low on Tuesday. However, shower/storm motions will be parallel to the aforementioned stalled frontal boundary and look to support training convection which is expected to result in a period of soaking rainfall especially across our southern CWA. Since the anticipated rain amounts of 1.0-1.5 inches are expected to fall over the course of 24-36 hours, the threat for flash flooding does look to be low. Though, the rainfall may still lead to river rises and localized ponding issues in lower- lying areas.

The widespread rain is forecast to start tapering Tuesday night into Wednesday as the shortwave pivots into the eastern Great Lakes and the front drifts into the Ohio River Valley. While this should give us a reprieve for Wednesday, another shortwave is progged to pivot into the Great Lakes Wednesday night into Thursday which should allow for additional rain showers to develop. With the frontal zone expected to be stalled near the Ohio and Tennessee River Valleys the better coverage of showers (and thunderstorms) should focus to our south, but cannot fully rule out some glancing showers in our southern CWA on Thursday. Regardless, broad troughing is expected to return to the Great Lakes next week which will keep temperatures near to below average with daily highs in the 50s to near 60 and overnight lows in the 30s and 40s Tuesday onward. This pattern will also support occasional rain chances into next weekend as shortwaves pivot through the pattern, but details on exactly when and where these waves will go remain uncertain at this range.

Yack

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1221 PM CDT Sat May 2 2026

Key Messages:

- Lake breeze likely not to impact the main Chicago terminals this afternoon.

- Brief period of scattered showers possible Sunday morning.

- Increasingly gusty southwest winds on Sunday.

A lake breeze boundary has developed again near the lake early this afternoon. While it will attempt to move inland across northeastern IL this afternoon, westerly surface winds farther inland are expected to remain just strong enough to keep it east of ORD and MDW through the day. Accordingly, unlike the past couple of afternoons, we do not anticipate an easterly wind shift at the ORD or MDW today. Expect the winds to turn light from the southwest this evening and tonight, then ramp up and becoming increasingly gusty on Sunday as the surface gradient strengthens in advance of an approaching surface frontal trough. The strongest southwesterly wind gusts are expected to be up to ~30 kt from midday into the afternoon.

A quick moving weather impulse is also expected to track across the area Sunday morning. As it does, a brief period of rain showers could materialize across portions of the area Sunday morning. We thus continue to highlight this potential with a PROB30 from 14 to 17 Z Sunday. Otherwise, VFR conditions are anticipated through the period.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 7 AM to 7 PM CDT Sunday for the IL and IN nearshore waters.