textproduct: Chicago

KEY MESSAGES

- Windy Thursday with southerly winds gusting 40-45 mph.

- Strong to severe thunderstorm threat (level 2 out of 5) ahead of a cold front Thursday afternoon/evening.

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

DISCUSSION

Issued at 304 AM CDT Wed Apr 1 2026

Through Friday:

An active weather pattern is expected to continue through Saturday before a period of quieter weather is anticipated into early next week. Of particular interest in this pattern, is the threat for another round of severe thunderstorms, particularly Thursday afternoon into the evening.

The surface cold front from yesterday has settled into southern parts of IL. It will stall in this region for a period today before lifting back northward tonight into Thursday morning in association with the next quickly developing Plains cyclone. In spite of the southern placement of the surface front, warm air advection aloft over this frontal boundary is expected to continue to generate showers and some non-severe thunderstorms across a west-to-east corridor from Missouri eastward across central IL and IN. It appears the more persistent showers today will occur along and south of I-80 this morning in advance of an approaching low amplitude impulse tracking eastward through the Midwest. Shower coverage should then be on a decreasing trend through the afternoon.

We cannot rule out a few showers making there way as far north as the Chicago metro area later this morning into the early afternoon. However, much of the area north of I-80 should see a good amount of dry time today, albeit with cloudy and cool conditions. Blustery east-northeasterly winds, gusting up around 30 mph will promote a much cooler day, particularly along and near the Lake Michigan shore, where temperatures today will remain in the low 40s. Farther inland, conditions won't be much better, with cloudy and breezy weather only supporting temperatures into the mid to perhaps upper 40s well south and inland.

Attention quickly turns to the next shortwave trough, currently noted in the water vapor imagery moving onshore across California. This wave will eject eastward across the Four Corners region of the Desert Southwest through the day, before transversing the CO Rockies and inducing lee cyclogenesis over the central Plains this evening. Thereafter, the parent surface cyclone is favored to track northeastward across the Mid- Missouri Valley on Thursday, then into the Upper Great Lakes late Thursday evening and night. As it does, the remnant frontal boundary, stalling today across downstate IL, will shift back northward across the area as a warm front Thursday morning, setting the stage to a return to more active weather locally tonight and on Thursday.

Waves of showers and embedded thunderstorms are expected to develop tonight north of the surface warm front as a strengthening southerly low-level jet ramps up moisture advection over the frontal boundary. This activity is expected to overspread our area for a period tonight into early Thursday morning. Very low clouds and possibly even some fog may also briefly develop north of the warm frontal boundary for a period early Thursday morning. Once this boundary finally shifts north of the area (may become briefly hung up along the northeastern IL lake shore through late morning or early afternoon) developing gusty south winds (potentially gusting to or even a bit in excess of 40 mph) will push temperatures back to 60s and 70s as surface dewpoints surge into the lower 60s.

The main concern on Thursday continues to revolve around the threat for severe thunderstorms, particularly in the afternoon and evening as the potent spring cyclone tracks northeastward across northeastern IA into WI. As is typical with such a system this time of year, deep layer low- to mid-level south- southwesterly flow in excess 60 kt will result in very impressive kinematics across the area. It also appears that the very moist warm sector (low 60s dewpoints) will foster ample afternoon destabilization, despite the likely presence of extensive cloud cover and even ongoing rounds of morning and early afternoon convection. This initial convective activity on Thursday may end up being the remnants of overnight convection to our southwest. Assuming adequate destabilization is able to occur in advance of the cold front and area of low pressure shifting into northeastern IA, conditions will be favorable for severe thunderstorms, including a threat of tornadoes. Accordingly, the SPC conditions to highlight our area in a level 1 out of 5 severe risk for Thursday. Expect the threat of storms to persist with the cold front through early to mid Thursday evening, before the activity wanes with the cold frontal passage. In addition to the severe threat, we will also have to keep an eye on the threat for any localized flooding from the heavy rainfall expected to accompany these storms.

In the wake of Thursday's system, we do look to briefly dry out late Thursday night into early Friday. However, another storm system will be quickly developing and approaching the area later in the day Friday, with more heavy rain producing showers and storms expected into Saturday morning.

KJB

Friday Night through Tuesday:

The upper trough/low that currently sits off the coast of the Pacific Northwest is forecast to be ejecting into the central Plains by Friday evening. As it does so, a surface low is expected to be developing in eastern KS and western MO that will then begin to lift towards the Mississippi Valley Friday night into Saturday. The approaching surface low is expected to lift the stalled frontal boundary forecast to be in central IL/IN back northward as yet another warm front bringing with it an additional period of showers and thunderstorms. However, the projected track of the surface low from northern MO to southern WI Friday night looks to limit the northward extent of the warm front before the system's cold front is ushered through northern IL and northwest IN early Saturday morning. While this likely won't do much to limit the coverage of rain, it may limit the amount of instability that is able to build into the area and thus make the coverage of thunderstorms a bit less especially for further north in our CWA. That said, if sufficient instability can materialize Friday night, then a localized strong to severe storm threat could develop given the 40-45 kts of shear forecast to be present.

Regardless of the storm coverage/intensity, widespread rain is likely Friday night through Saturday as this system moves through. While the system is forecast to be rather progressive, the nearly continuous rounds of rainfall leading up to this event will make conditions favorable for some localized flooding issues before rain ends Saturday evening. Outside of the rain, temperatures on Saturday are also expected to be cooling through the day in the wake of the cold front. So be prepared for the warmest temperatures to occur early before they dip into the 40s by Saturday evening.

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 THURSDAY/

Issued at 633 AM CDT Wed Apr 1 2026

Forecast concerns for the terminals...

- Off and on drizzle/sprinkles through this afternoon with a 20-30% chance of showers. - Widespread rain showers and embedded thunderstorms this evening and overnight which could result in IFR ceilings and visibilities.

- Breezy northeast winds gusting around 20-25 kt through tonight with MVFR ceilings. Winds become southwesterly Thursday morning with gusts up to 25-30 kts.

A broad area of showers and embedded thunderstorms continues to drift across northern MO and central IL/IN this morning with sprinkles and drizzle being noted on the northern fringes of the precipitation band. While periods of sprinkles/drizzle could move across the terminals through this afternoon, it seems the better chance for any true showers will hold off until late this afternoon and evening (20-30% chance). The best coverage of rain will occur this evening as the frontal zone in central IL/IN lifts back north as a warm front. Once this rain arrives it is expected to persist through tonight with chances for embedded thunderstorms at times especially after midnight (20% chance). The more convective showers/storms after midnight may also result in periods of IFR ceilings and visibilities through early Thursday morning.

Outside of the rain, winds will remain breezy out of the northeast today with gusts around 20-25 kts. Ceilings will also continue to lower back to MVFR over the next couple of hours where they are expected to remain through the rest of the forecast period. The exception, however, will be at RFD where lower-end VFR conditions look to prevail through this afternoon.

Heading into Thursday, it appears that any showers/storms overnight should gradually diminish by mid-morning before the main cold front moves through Thursday afternoon and brings additional chances for showers and thunderstorms. However, confidence on whether or not rain actually stops is low and thus have maintained a VCSH through the end of the 30-hour TAFs. Furthermore, ceilings may also attempt to rise if rain stops Thursday morning but this too is low confidence. Regardless, winds will become more southeasterly Thursday morning with gusts increasing into the 25-30 kt range.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CDT Friday for the IL and IN nearshore waters.