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.

MESOSCALE

Issued at 1116 AM CDT Tue Mar 31 2026

The morning thunderstorm activity has and will continue to perturb the background mesoscale environment. There are two main corridors of concern in the near term are along and southeast of Interstate 57. We are seeing occasional rear inflow jet development on a few cells, but nothing substantial. While we cannot rule out a few instances of quarter size hail, the main hazard in the near term would be winds to 40 mph and smaller hail, particularly the cell in Iroquois county. The messy complex of storms ahead of this cell would suggest that intensification is less likely.

The second area of concern is along and ahead of the cold front in northwest Illinois. The environment here is less disturbed, and characterized by 30-35 kt of effective shear, mid level lapse rates in excess of 8 deg/km, and narrow axis of increasing DCAPE (a parameter that help diagnose the potential for damaging winds). We are seeing some development along the front, though surface instability is still capped at the moment. These steeper lapse rates will spread back in from the west this afternoon along the back edge of the cloud shield in western Illinois.

For the remainder of the area, including across most of the Chicago metropolitan area, the atmosphere pretty unfavorable to severe weather, with weak mid and low level lapse rates, at least for the next few hours. Thunder coverage will be lower for the next few hours, though expect at least isolated thunder.

The front will be the area to monitor for redevelopment of thunderstorms this afternoon and evening. At this time, the severe threat still looks to be focused along and south of I-80 and into central Indiana.

With all that said, we are going to ride the severe thunderstorm watch as-is for a little bit here to reassess the atmosphere and how recovery will take place, however we did want to highlight that the early afternoon hours will likely be a lull in severe weather potential.

KMD

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 /12Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 625 AM CDT Tue Mar 31 2026

Forecast concerns for the terminals...

- Two rounds of showers and thunderstorms today both of which could contain strong to severe thunderstorms capable of gusty winds and large hail.

- First round of showers/storms 13z through 17-18z, second round after 21z this afternoon with a cold front.

- Cold front to result in a northerly wind shift this evening followed by a MVFR ceilings overnight.

A shortwave disturbance is traversing across eastern IA this morning which is starting to generate a line of scattered showers and thunderstorms. This line of showers/storms is expected to move through the Chicago area terminals around 13z and will last for at least 2-3 hours before exiting the area after 17z. While the biggest concern with the morning storms will be lightning and heavy rainfall resulting in lowered visibilities, a few storms could become strong to severe and produce gusty winds to 50 kts and large hail up to half dollar size. After the morning round of storms exits a brief break in the weather is expected before a second round of showers and thunderstorms moves in with the cold front that is currently in southeast MN. This second round of showers and storms should have broader coverage than the first round and will once again contain the potential for severe weather in the form of gusty winds and hail.

Outside of any showers/storms today, BKN to OVC VFR skies are expected with breezy southwest winds gusting around 20-25 kts. However, there has been a surge of locally higher gusts within the band of rain showers moving across northern IL which could result in a brief period (up to an hour) of 30+ kt gusts.

Behind the cold front this evening, winds will initially turn north-northwest before becoming northeasterly after 00z this evening. Gusts overnight look to remain in the 20-25 kt range especially at the Chicago area terminals but DPA and RFD could lose the gusts for a period. Otherwise, expect ceilings to lower to MVFR behind the front and remain as such through the end of the TAF period.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

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