textproduct: Chicago

KEY MESSAGES

- Waves of showers and storms expected today. Some of the storms this afternoon may become severe. There is also a threat for tornadoes between 5 and 9 PM CST, especially along/west of I-39.

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

- There is another threat for severe weather Friday and Saturday, 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.

DISCUSSION

Issued at 324 AM CDT Thu Apr 2 2026

Forecast concerns continue to focus on the threat of showers and thunderstorms, some of which are likely to become severe this afternoon and evening. Outside of thunderstorms, strong southerly winds are also expected to develop as a warm front lifts north across the area later this morning. With gusts expected to be in the 45 to 50 mph range for a period today, we have opted to hoist a wind advisory for all but far northwestern IL for this afternoon through early evening.

Early this morning, a large region of showers, and embedded non- severe thunderstorms, continue to stream northeastward across the Midwest into our area in advance of a rapidly maturing surface cyclone over western Kansas. It appears the primarily corridor for these showers and storms this morning will primarily be focused along and northwest of the I-55 corridor, with more scattered activity farther to the southeast. Warm rain processes appear to be aiding in the efficiency of this activity to produce localized heavier rainfall rates and amounts. In fact, some of the recent MRMS precipitation estimates indicate the presence of narrow southwest-to-northeast corridors of nearly inch per hour rates with some of this activity currently lifting into northern IL. While this does not look to materialize into a significantly flooding threat across northern IL this morning, the continued likelihood for locally moderate to briefly heavy rainfall may result in some minor flooding, particularly in ditches and low spots. Significant ponding can also be expected on area roads into the morning commute.

The parent surface cyclone will track northeastward today, generally along a corridor from far northwest MO late this morning, across northeastern IA into southwestern WI late this afternoon into early this evening. As it does, the surface frontal boundary in place across far southern IL will race northward as a warm front this morning. A period of very low clouds, and possibly even a short period of fog, will be likely early this morning just ahead of the warm frontal boundary. Otherwise, while the front may not clear far northeastern IL until sometime early this afternoon, a majority of the area will become entrenched within the windy, warm and very moist warm sector of the cyclone for the afternoon and evening hours today. Strong southerly winds in the warm sector will push temperatures into 60s and low 70s this afternoon as surface dewpoints surge into the low to mid 60s. Also, as mentioned above, the likelihood of gusty southerly winds up to 45 to 50 mph this afternoon did prompt us to hoist a wind advisory for all but far northwestern IL. The current advisory is set to end at 7 PM this evening, though rather gusty southwest winds may continue beyond this time.

In the wake of this mornings showers and storms, a narrow corridor of destabilization is expected to expand northward into eastern IA and northwestern IL, just in advance of the surface low and beneath the region of better mid-level height falls/cooling associated with the approaching negatively tilted impulse. This is expected to foster ample conditions for additional scattered surface based storm development by mid to late this afternoon across eastern IA, just ahead of the approaching cold front. The kinematic environment in which the storms develop will favor supercells, and the oblique orientation of the deep layer shear vector relative to the surface front suggests these initial storms may be semi-discrete for a time as they progress into northwestern IL. The presence of strong low-level wind shear will also favor tornadoes with these storms into early this evening. The greatest tornado threat late this afternoon into early this evening expected from eastern IA into northwestern IL and southwest WI. This area matches very well with the current SPC day 1 10% tornado threat area. These storms should progress eastward across northern IL into a region of weaker instability. In spite of this, a continued severe threat, possibly transitioning more to damaging wind gusts with isolated tornadoes, may persist for a few hours in the evening due to the strongly favorable kinematic environment ahead of the front. The storm threat will end from west-to-east through the evening.

These late afternoon and evening storms should have the greatest severe risk for the area (including tornadoes). However, there may end up being a localized damaging wind risk across much of northern IL with some of the early to mid afternoon (1-4pm) storms expected to move across the area well in advance of those talked about above. These storms should become nearly surface based and rooted in the warm sector early this afternoon, and hence have access to 50+ kt winds not too far above the surface. Locally heavy rainfall will also likely accompany these storms.

KJB

Friday into Saturday:

Forecast thinking during this period has not changed from previous thinking.

Yet another upper-level shortwave is poised to dive into the central Plains tonight into Friday, causing the cold front this evening to stall somewhere in the Ohio River Valley Friday. A surface pressure col will move over the area Friday morning before pressure falls in the Midwest allow for southerly flow to redevelop and the warm front to lift back northward. Exactly how far northward the front will retreat is an item of low confidence, and will be important to the forecast for temperatures by mid-afternoon. In scenarios where the front gets hung up somewhere across central Illinois and Indiana, many areas may remain in the 50s for much of the day. Meanwhile, any areas south of the front will have the potential to jump back up into the 70s.

Friday afternoon, forecast soundings depict minimal capping along the warm front leading to concerns for the development of convection. With the upper-level wave remaining well to our west, shear profiles along the front will be modest and largely driven by low-level directional changes across the front itself. Taken together, the conceptual pattern appears supportive of low-topped supercell structures with a threat for funnel clouds and weak tornadoes along the warm front. At this point, the front is favored to be somewhere south of I-80, and perhaps even south of US-24. Pin-pointing the location of the front will be a priority in future forecast packages.

The upper-level shortwave is expected to shift eastward into the Great Lake Friday night into Saturday likely accompanied by a band of showers and thunderstorms. The unfavorable diurnal arrival time of the peak forcing suggests the severe weather threat should be low in our area, though any slowing of the wave would be cause for concern for one last window of severe thunderstorms in our area (This stretch from mid-March through now has been relentless!). At any rate, Saturday will feature nearly steady temperatures in the 50s to around 60 as cold air advection works into the region behind the cold front.

Borchardt

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 /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 632 AM CDT Thu Apr 2 2026

Forecast concerns for the terminals...

- Periods of showers and low IFR ceilings will persist through the morning. Occasional lightning strikes will also be possible especially in northwest IL.

- 30-40% chance for a 2-3 hour period of fog mid to late morning which could result in sub-mile visibilities and LIFR ceilings. - Additional rounds of showers and thunderstorms this afternoon and evening, some of which will be severe with damaging winds, hail, and tornadoes possible.

- Strong non-thunderstorm winds this afternoon gusting 30-40 kts from the south-southwest.

An upper trough continues to eject eastward towards the Mississippi Valley this morning with its surface low now observed in southwest IA and northern MO. A warm front extends from this surface low eastward across central IL and IN. Ahead of these features, continued warm advection atop the frontal zone has maintained a broad area of showers overnight and that will continue through the morning. While forecast soundings do show instability increasing after daybreak, confidence on the coverage of thunderstorms this morning remains somewhat low so have opted to forego a formal thunder mention in the TAFs except for at RFD where confidence is slightly higher. That said, some occasional lightning strikes will be possible with any showers this morning.

Outside of the showers this morning, IFR ceilings are expected to prevail as the colder air mass overhead continues to saturate the low-level moisture lifting northward with the warm front. In fact, as the warm front moves into the area towards mid-morning (14-16z) some fog is expected to develop which could result in a 2-3 hour period of sub-mile (as low as 3/4 to 1/2 SM) visibilities at the terminals. While this trend has been noted upstream in eastern MO and central IL, confidence on how dense any fog will be remains low so for now have opted to introduce a 1 SM TEMPO in the TAFs.

Heading into this afternoon, the surface low and its trailing cold front will begin to move into northern IL and northwest IN which should result in an uptick in shower and thunderstorm activity with at least two rounds of storms expected. The first round is forecast to occur between 20z and 23z with the second expected from 00z through 04z. Both of these rounds will be in an environment favorable for severe weather in the form of damaging winds, hail, and even tornadoes. Though, the better tornado environment is still forecast to be largely in northwest IL. In addition to the storms, strong non-thunderstorm winds are expected this afternoon with gusts peaking in the 30-40 kt range through 00z.

Once the system's cold front moves through this evening, the shower and thunderstorm threat will diminish and give us a period of dry weather for tonight. However, MVFR ceilings are expected to redevelop this evening and look to persist through at least daybreak before attempting to scatter out Friday morning. Confidence on when/if skies scatter is low but opted to lean optimistically in the TAFs due to shallow moisture depths noted in forecast sounds. Winds overnight also look to slowly diminish with gusts around 20-25 kts out of the west before gusts fully subside Friday morning.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory from 1 PM this afternoon to 7 PM CDT this evening for ILZ006-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Wind Advisory from 10 AM this morning to 7 PM CDT this evening for ILZ023-ILZ032-ILZ033-ILZ039.

IN...Wind Advisory from 10 AM CDT /11 AM EDT/ this morning to 7 PM CDT /8 PM EDT/ this evening for INZ001-INZ002-INZ010- INZ011-INZ019.

LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL and IN nearshore waters.

Small Craft Advisory from 9 PM this evening to 4 AM CDT Friday for the IL and IN nearshore waters.

Gale Warning from 1 PM this afternoon to 9 PM CDT this evening for the IL and IN nearshore waters.