textproduct: Chicago

KEY MESSAGES

- Scattered severe thunderstorms through mid evening with a tornado potential, highest along/west of the Fox Valley.

- Strong gusty south winds, gusting at times to 45-50 mph are expected this afternoon, outside of thunderstorms.

- There is another threat for severe thunderstorms Friday afternoon through Saturday morning, though the threats are conditional on placement of boundaries and system arrival timing.

- A transition toward a quieter, but cooler, pattern is on track to arrive early next week.

MESOSCALE

Issued at 203 PM CDT Thu Apr 2 2026

A couple of different convective regimes with accompanying severe threat late this afternoon into this evening. The most obvious is with rapidly develop intense convection across northern MO into southern IA in the quickly destabilizing warm sector. There is some uncertainty with respect to the eventual extent of coverage with this convection, but whatever there is would likely begin to get into our western CWA early this evening. By the time it approaches, there will likely be some slight decrease in MLCAPE and corresponding slight increase in MLCIN after sunset. If the convection is well organized or intense, then those subtle changes in boundary layer instability may not be a terribly detrimental factor with respect convective intensity, at least not initially. If convection is a bit weaker or less organized, then the subtle instability changes could result in weakening as this convection approaches or gets into our western CWA.

The second potential convective regime, which is lower confidence, is that the current elevated convection over western IL could become rooted in the boundary layer this afternoon. The 18z KILX sounding depicted noteworthy warm layer near 500mb, however mesoanalysis data has 500mb temps 2-4C colder upstream. As these cooler mid-level temps advect east across Illinois this afternoon, that should result in a corresponding increase in instability. Certainly seems plausible that as this occurs, that the currently elevated storms over western IL could increase in coverage and eventually become rooted in the boundary layer. This change in the inflow layer of the storms would also result in marked increase in storm intensity/severe potential.

Area VWPs depict a very impressive kinematic profile all across the region. So any boundary layer rooted convection that does become sustained would likely become supercellular, at least initially. The very large 0-1km looping hodograph with strong streamwise vorticity would support a threat for tornadoes with any sustained strong supercells either with the upstream activity over IA/MO or if the elevated convection becomes rooted in the BL this afternoon over IL.

There is still somewhat low confidence in which, if either, convective scenario will occur with a severe weather threat in CWA, the environmental shear profiles means that we will need to closely monitor convective trends closely this afternoon.

- Izzi

DISCUSSION

Issued at 242 PM CDT Thu Apr 2 2026

Specific severe potential discussed above in the recent mesoscale discussion but more broadly, low pressure over southern IA will move northeast across southern WI this evening. A warm front is currently lifting north across far northern IL with temperatures warming into the upper 60s/lower 70s and dewpoints generally in the lower 60s. Current thunderstorms across far northwest MO/southwest IA are expected to continue moving east/northeast through the afternoon and into northwest early by early evening. Cams have generally been in good agreement with the current activity along the I-39 corridor slowly increasing in coverage and intensity. They have also been in fair agreement with additional development along/east of I-57 and will need to monitor for the potential for additional thunderstorms developing across this area. Any of the thunderstorms that develop will have the potential to be severe.

Southerly winds have steadily increased south of the warm front and further increasing winds are possible with gusts to 45 mph. While the best potential for these higher gusts may be generally south of I-80, have maintained the wind advisory as is until its expiration at 00z.

Southeast winds ahead of the cold front will allow for areas of fog across far northeast IL for the next hour or two until the warm front lifts north into southern WI.

The showers and storms will end from northwest to southeast this evening into the early overnight hours, with dry conditions then expected through at least midday Friday. A warm front is expected to lift north to about I-80 on Friday while northeast winds gradually increase north of I-80. There is a chance of showers and thunderstorms Friday afternoon, mainly in the warm sector, but confidence is low for trends and maintained chance pops for much of the area, mainly in the late afternoon. It appears the best chance for showers and thunderstorms will be later Friday evening through Saturday morning ahead of a strong cold front. The front looks to be east of the area by mid morning Saturday, ending any severe threat, but there may be lingering precipitation through midday Saturday. cms

Sunday Onward:

In the wake of this system, a period of drier weather is expected to close out the weekend as a surface high moves into the Mississippi Valley. However, the upper trough is expected to stall over the Great Lakes which will result in nearly constant northwest flow resulting in seasonably cool high temperatures in the 40s to lower 50s for Sunday and again on Monday.

The upper trough is forecast to start pushing east of the Great Lakes on Monday as an upper ridge builds over the central CONUS. As a parting gift a final shortwave is progged to round the backside of the trough Monday night which could bring us one more period of rain showers during this timeframe, That said, there is a lot of variability in guidance as to how much moisture will be available Monday night as the wave moves through so there is a chance that the rain avoids northern IL and northwest IN all together. For now though will advertise a 20-40% chance for rain. After Monday night, the upper ridge will be moving into the Great Lakes which will promote dry conditions for the middle of next week with temperatures moderating towards more seasonable values in the mid to upper 50s.

Yack

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 705 PM CDT Thu Apr 2 2026

Key aviation messages:

- Broken line of strong to severe storms to move across the area this evening.

- Periods of IFR CIGs possible overnight through the day on Friday (confidence in trends remain low).

- Gusty S to SW winds tonight easing toward daybreak, then turning NE to E by midday Friday.

- Another round of SHRA (possible TS) may occur Friday evening.

Focus in the immediate near term is on the broken line of strong to severe thunderstorms moving across the local area this evening. Have focused TEMPO groups for TS at RFD through 1Z, 1-3Z at ORD/MDW/DPA, and 2-4Z at GYY. Primary hazard with these storms will be damaging wind gusts. A brief tornado also cannot be ruled out.

Winds ahead of the storms will remain strong out of the south (170-190 degrees) with peak gusts in the 35-40 kt range. Winds then ease (albeit still gusty) and turn southwest in the wake of the storms and associated cold front. We lose the gusts toward daybreak on Friday eventually flopping east northeast toward midday (likely paired with a lake breeze) and increasing again into the 10-15kt range through the afternoon.

Ceiling trends through the rest of the period are lower confidence overall with a signal for IFR stratus possible overnight and for much of the day on Friday. The period with slightly higher confidence in low-end MVFR to possible IFR will be overnight in the wake of the cold front. Have introduced TEMPO IFR at RFD but have kept the Chicago area terminals MVFR for now given lower confidence in coverage. Additional low stratus may move overhead in the wake of the lake breeze and persist into the evening.

Lastly, another round of showers and possible embedded storms may lift into the area late Friday afternoon and through the evening. Have accounted for this with PROB30 groups for heavier showers but an introduction of thunder may be warranted with later updates.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory until 7 PM CDT this evening for ILZ006-ILZ010- ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032- ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory until 7 PM CDT /8 PM EDT/ this evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning until 9 PM CDT this evening for the IL and IN nearshore waters.

Small Craft Advisory until 4 AM CDT Friday for the IL and IN nearshore waters.