textproduct: Chicago

KEY MESSAGES

- Afternoon showers/storms expected to wane into this evening.

- Another round of showers/storms possible tonight (20-30%), including the potential for severe storms and heavy rainfall.

- Additional strong/severe storms possible Wednesday.

DISCUSSION

Issued at 310 PM CDT Tue Aug 11 2026

Ongoing scattered showers and storms will linger this afternoon and early evening in the wake of significant severe weather earlier today. This activity is expected to wane over the next several hours with convective inhibition/subsidence in place across the CWA as the reinforced surface boundary has pushed south of the area across central Illinois.

While this will likely lead to a lull in shower/storm chances this evening, additional thunderstorm development will be possible overnight tonight -- primarily across northeast Illinois/northwest Indiana, including the Chicago area. The aforementioned boundary is expected to work back north across the area with time this evening with showers/storms possibly training along/north of said boundary. Strong buoyancy aloft on the order of 3,500+ MUCAPE combined with deep-layer shear ~35 kts will support a continued threat for strong/severe storms tonight. Given anticipated convective evolution/training of storms, perhaps of equal concern will be the potential for heavy rainfall/flooding later tonight. Storms in an environment characterized by ~2" PWATs would lead to very efficient rainfall, and potentially bring an additional 1-2"+ of rain to areas that already saw heavy rainfall earlier in the day. While uncertainty remains relatively high at this time (20-30% PoPs tonight), another round of impactful storms remains possible tonight.

The aforementioned boundary is expected to remain draped across the area during the day Wednesday with ample instability in place along and to its south, supporting continued thunderstorm chances Wednesday morning into Wednesday evening. Damaging winds will be the primary threat with strongest storms, especially if another line organizes and tracks from northwest to southeast across the warm sector south of the front during the day. Hail and locally heavy rainfall will also be possible.

Precise details in regards to timing and impacts becomes more obscure beyond Wednesday, but additional rounds of thunderstorms will be possible into the end of the week as the boundary lingers across the area and keeps a warm, moist airmass in place with relatively strong northwest flow aloft. A more substantial break in storm chances may not come until late this upcoming weekend or early next week as surface high pressure may settle more firmly over the Midwest.

Cornish

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/

Issued at 1253 PM CDT Tue Aug 11 2026

Mainly VFR conditions this afternoon, but do expect redevelopment at some point (already seeing some across IA as of 1740z) and will need to monitor this for the rest of the afternoon. Currently have VCTS in for 23z-2z timeframe for this idea. Winds likely go light overnight with cigs trending down with potential for LIFR conditions esp toward daybreak, whether FG/BR or low stratus...and think this will try to mix to VFR again toward daybreak. Not impossible there could be another round of TSRA between 6-12z but very low confidence in this attm. Winds primarily light and E/NE thru period but could go more S at GYY if lake/land breezes develop.

LOT WATCHES/WARNINGS/ADVISORIES

IL...Lakeshore Flood Warning until 5 PM CDT this afternoon for ILZ104.

IN...Lakeshore Flood Warning until 5 PM CDT this afternoon for INZ001-INZ002.

LM...None.