textproduct: Chicago

KEY MESSAGES

- Scattered thunderstorms tonight (40-50% chance) with some storms possibly severe with damaging winds and large hail.

- Scattered thunderstorms Tuesday afternoon/Tuesday night with some storms possibly severe in the afternoon/evening, ahead of a strong cold front/rapid temp drop.

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

DISCUSSION

Issued at 204 PM CDT Mon Mar 30 2026

High temps are expected to top out in the mid/upper 70s this afternoon with a few locations tagging 80. Southwest winds may increase further through sunrise, perhaps with gusts into the 35 mph range. As low level winds increase this evening and surface temps only drop in the lower 60s tonight, the low levels will likely stay partially mixed, allowing for gusts overnight in the mid/upper 20 mph range at times.

An upper level wave now moving across the central Plains will move across the local area later this evening into the overnight hours. The models differ considerably on convection with this system. There is the potential for thunderstorms to develop across east central IA and then move east across the area later this evening, likely in a slowly weakening mode. There is also the possibility that additional thunderstorms develop right over the local area. While lapse rates and instability are sufficient for strong to locally severe thunderstorms, the limiting factor appears to be the amount of moisture in the low levels and whether it will be high enough for storm formation. HRRR/RAP are very consistent with thunderstorms developing in the late evening and moving east through the overnight hours, with a focus along/north of I-80. While there is still uncertainty for coverage, have high chance pops in the 40-50% range for this potential tonight. If thunderstorms develop, the strongest storms may produce large hail and locally damaging winds. And while nighttime cooling may be a limiting factor, as noted above, the warmer temps tonight will likely keep the low levels partially mixed and allow for any stronger storm wind gusts to reach the surface.

While the earlier timing (late evening/overnight) seems to be the trend, there does remain uncertainty for timing and whether convection will be ongoing at/after daybreak Tuesday morning and if so, how that plays into precipitation trends for Tuesday. For now have trended pops lower for Tuesday morning which then should allow for a decent temp recovery, with temps likely in the low/mid 70s by midday, eventually warming further to the upper 70s, possibly near 80 south of I-80.

A strong cold front will move across the area Tuesday afternoon through Tuesday evening, shifting winds northerly, and eventually northeasterly. This will allow for a rapid temp drop behind the front, most pronounced near Lake Michigan. Still some uncertainty for the timing of this front but mid afternoon for the Chicago metro/lakeshore seems plausible but this may also be too slow. An even faster fropa could impact high temps across the northern cwa.

Scattered thunderstorms are expected to develop ahead of this cold front Tuesday afternoon, perhaps as early as late Tuesday morning, depending on timing, with the convection spreading southeast across the area through the afternoon into the evening. Strong to severe thunderstorms are possible during this time period but overall confidence for severe weather is low at this time with the best potential likely south of I-80. Heavy rain and possible localized flooding will also be possible during this time, also likely focused south of I-80. There is also uncertainty for how fast this activity will move southeast of the local area. The GFS/NAM show elevated convection continuing through Wednesday morning and even suggest it will slowly lift north back across the area. While this activity may not be heavy thunderstorms, the potential long duration, training and persistence may also lead to localized flooding concerns.

There may also be fog along/behind the cold front Tuesday afternoon into Tuesday evening and especially over Lake Michigan though confidence is too low to add mention at this time.

Confidence for precip trends/timing Wednesday is rather low and dependent on the trends from Tuesday night. The expectation would be for the warm front to slowly lift back north Wednesday afternoon into Wednesday night, though there is still timing uncertainty. But as this warm front lifts north, precip should be ending from south to north. Too much uncertainty from this distance to try to time this out and its possible much of the local area will see showers/drizzle and perhaps a few storms through Wednesday afternoon. After morning lows in the 30s for much of the area, highs may only rebound into the 40s for areas north of I-80 along with breezy northeast winds gusting into the mid 20 mph range.

Depending on the overall timing of the warm front, its possible that much of Wednesday night could end up being dry with temps warming through the night, especially across the northern cwa. This would then setup a potentially warm Thursday with highs back at least in the 60s north and likely 70s south. Thursday may also be fairly windy with southerly winds possibly gusting into the 30-35 mph range.

Low pressure is expected to move just northwest of the area Thursday afternoon into Thursday evening with a cold front moving across the area Thursday night. Additional thunderstorms will be possible during this time and while currently not outlooked, the potential does exist for a few strong to possibly severe thunderstorms during this time period.

The daylight hours on Friday may bring a short lull in the active pattern before another storm system moves across the region bringing showers and scattered thunderstorms with the best timing for this activity looking to be Saturday. Another cold front passes the area Saturday night with a period of cooler temperatures through early next week. cms

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1213 PM CDT Mon Mar 30 2026

Broad surface troughing across the central United States will maintain southwesterly winds (occasionally gusting above 25kt) through this evening. Tonight, pressure falls in the Great Lakes will facilitate the development of a strong southwesterly low- level jet, with 925 to 850mb flow increasing to 50-55 kt. Even with mild surface temperatures supporting at least occasional surface southwesterly gusts to 25kt through the night (mainly at at ORD/MDW), LLWS criteria will be met at all terminals through daybreak Tuesday.

The overarching pattern tonight through tomorrow will be supportive of multiple waves of showers and thunderstorms in the general region.

The first opportunity for convection will be generally between 04-10Z late tonight as an upper-level vorticity maxima currently moving across central Nebraska shifts eastward and activates an EML plume stretching across the Great Lakes. Coverage of convection overnight will depend on the degree of moistening at the base of the EML, with plausible scenarios ranging from isolated cells near the IL/WI state line to an outright convective complex moving across the terminals. Environmental conditions will be favorable for strong westerly winds with convection, especially if any upscale growth occurs (in which case, gusts >50kt would be possible). Will cover the threat for convection tonight with PROB30 groups at all terminals with an opportunity to upgrade to TEMPO groups in later TAF packages as trends emerge.

The continued interaction of isentropic ascent with the EML plume may maintain clusters of thunderstorms after daybreak, particularly near DPA/ORD/MDW/GYY. Confidence in convection continuing after daybreak is on the lower end of the spectrum, with a completely dry scenario being equally plausible. Will go ahead and introduce PROB30 groups at all but RFD through 17Z. Am cautiously optimistic that there will be a break in convection during the early afternoon hours before another upper-level wave rides into the region toward the end of the TAF period and encourages new convective development. Winds tomorrow will be southwesterly with occasional gusts in excess of 20 kt,

At ORD/MDW, a lake-enhanced front will shift across the terminals during the last 6 hours of the TAF period bringing a northeasterly wind shift and IFR to MVFR cigs.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES

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