textproduct: Chicago

KEY MESSAGES

- Scattered showers and thunderstorms today, with an afternoon and early evening threat for severe storms ahead of a strong cold front.

- An active pattern will continue through Saturday with periods of showers and thunderstorms.

DISCUSSION

Issued at 258 AM CDT Tue Mar 31 2026

Through Wednesday night:

The main focus this morning revolves around convective trends this morning into this evening.

A mid-level impulse currently tracking eastward across IA continues to drive an area of high based elevated convection eastward into northwestern IL early this morning. In spite of the elevated nature of this complex of storms, a rather dry sub-base cloud layer has actually supported the development of gusty surface outflow along the leading edge of the storms. Accordingly, it appears some gusty winds, perhaps as high as 40 to 50 mph will be possible with these storms as they progress eastward across northern IL (mainly near and north of I-80) through daybreak this morning. Also, cannot rule out some isolated instances of marginally severe hail, given the continued presence of steep mid-level lapse rates. However, any threat of severe weather with these early morning storms looks to remain isolated at best. Accordingly, we will be letting the ongoing Severe Thunderstorm Watch end.

Showers and storms may continue to fester across parts of northern IL for a few hours after daybreak this morning as the aforementioned mid-level impulse shifts eastward across the area. The severe threat with these storms is also anticipated to remain low and isolated at best. However, the main question becomes if and how this early morning activity, and any associated outflow, potentially impacts the favored placement and coverage of renewed strong/severe storms this afternoon.

The expectation is for additional scattered showers and storms to develop through the afternoon in association with a strong cold front shifting southward across the area through the afternoon. The prefrontal environment in which these storms develop is expected to be strongly sheared and unstable, particularly in areas that are able to amply recover from this mornings convection. While severe storms cannot yet be ruled out in any part of our area this afternoon, the better chances and coverage of them may end up more focused near and southeast of the I-55 corridor this afternoon and evening. We have to monitor observational trends this morning to see if this does end up being the better favored area. The primary threats with the strongest storms will again be large hail and damaging wind gusts.

Outside of the storms today, expect temperatures to drop through the 50s across far northern IL (even cooler lakeside) this afternoon in the wake of the frontal passage. A low stratus deck is also expected to overspread the area in the wake of the front late this afternoon and evening. Also cannot rule out a bit of fog as well flowing the front this evening.

The main focus for the more substantial showers and storms may briefly shift south of our area later tonight into Wednesday. However, confidence with precip trends and timing on Wednesday remain low at this time, owing to the timing of the next quickly organizing low pressure system across the central Plains. Nevertheless, Wednesday is looking to be rather cloudy and chilly day for the area as northeasterly winds dominant through the day. This is expected to hold temperatures in the 40s across much of northern IL, coolest near the lake.

Thursday through Monday:

A very active weather pattern is favored to persist across the Midwest into the Great Lakes region through Saturday. Within this pattern, ensemble guidance continues to favor the increasing potential for two additional storm systems to track northeastward through the western Great Lakes. While questions remain regarding the actual track and timing of both systems, there is an increasing signal supporting additional periods of showers and thunderstorms, particularly Thursday with the first system, and then again sometime Friday night into Saturday with the second system. The strong dynamic environment with each system, along with the nearly unabated access to deep moisture from the Gulf does add some concern for the occurrence of locally heavy rainfall and potential flooding. Accordingly, this is something that will need to be monitored over the next few days, along with any potential threat for strong to severe thunderstorms.

Following the second system slated to track across our region on Saturday, another push of colder air is anticipated for the second half of the weekend. Accordingly, a cooler day is anticipated for Easter Sunday, with highs likely only in the 40s to low 50s. This cooler weather also looks to persist into early next week.

KJB

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 1248 AM CDT Tue Mar 31 2026

Aviation forecast concerns for the 06Z TAFs:

- Periods of SHRA/TSRA overnight through Tuesday.

- Breezy SSW winds through midday Tuesday, shifting blustery NNE late afternoon with a cold frontal passage.

- MVFR/IFR cigs likely behind the cold front late Tuesday and Tuesday night, especially for Chicago terminals near Lake Michigan.

Midnight surface analysis depicts a nearly stationary frontal boundary from central MI/LM, west across southern WI into northern IA and NE. South of this front, breezy and mild conditions persist with south-southwest winds still gusting to around 20 kts at times. This should remain the case into the day Tuesday, before the front eventually pushes south as a cold front across the terminals in the afternoon, shifting winds to the north-northeast. These north-northeast winds will likely remain somewhat blustery into Tuesday night, especially in closer proximity to Lake Michigan for the Chicago terminals.

Back to the near term, high-res model guidance and current WSR88D VAD wind profiles indicate the strongest core of the low level jet has shifted east, easing to around 45 kts across the forecast area. Despite the surface gustiness, will maintain the mention of LLWS overnight with those 45 kt winds at around 2k AGL.

In addition, this southwesterly low level jet will maintain advection of moist air into the frontal zone north of the area, which will maintain the threat of periodic showers and thunderstorms overnight through Tuesday. One such cluster moved through the area last evening, while another is noted upstream across central/eastern IA in regional radar imagery. Timing the leading edge of this activity is around 07Z for KRFD and around 08Z or so in the Chicago metro area. High-res guidance does indicate some weakening of these storms toward morning, thus have maintained a PROB30 mention for now. Guidance also suggests additional development may occur over southwest IA in the next couple of hours, which could move into the area after sunrise. Not seeing signs of current development just yet, though models are in decent agreement of this, so have again maintained a PROB30 mention there as well. Did try to shorten up the PROB groups to some shorter windows for TS. A third round of potential TSRA is then depicted with/behind the cold front later Tuesday afternoon/early evening. HREF ensemble guidance indicates higher thunder probabilities in this time, and have included a TEMPO for those. Some showers may linger into the later evening/overnight hours especially south of the terminals. Low-level cold advection off of the lake may also produce a period of IFR/MVFR ceilings for the Chicago sites as well.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 7 PM CDT Wednesday for the IL and IN nearshore waters.