textproduct: Chicago

KEY MESSAGES

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

- Another round of showers/storms possible tonight (30-50%), 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 /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 145 AM CDT Wed Aug 12 2026

Key Messages:

- There is a low (~20-25%) chance for storms to affect the terminals overnight through early this morning.

- There is an increasing likelihood of storms affecting the terminals between mid-morning and mid-afternoon today. Strong to severe wind gusts will be possible with these storms.

- Lowered ceilings and possibly lowered visibilities are expected overnight through early this morning. LIFR/IFR conditions will be possible, especially at RFD, DPA, and GYY.

Isentropic ascent atop a surface boundary may attempt to initiate showers and storms near this boundary through the night. Thus far, convection has struggled to develop in northern Illinois. There may be a better chance for something to develop later tonight, but confidence in that is fairly low. It also appears that the surface boundary may remain far enough to the south and southwest of the terminals for any convection that develops near it to remain south of the terminals, so the probability of showers/storms affecting the terminals later tonight appears to be low enough (20-25%) to not carry any formal SHRA or TSRA mentions in the TAFs at this time. However, observational trends will need to be monitored closely, and it can't be ruled out that such a mention will need to be reintroduced into the TAFs at some point.

It appears that the best opportunity for storms to affect the terminals today will come between mid-morning and mid-afternoon as a convectively-enhanced disturbance associated with an organized thunderstorm complex in northern Nebraska approaches the area. Similar to yesterday, an organized bow or line of storms may develop and track through the area, producing swaths of severe wind gusts in excess of 50 kts. There is still some uncertainty in just how far north the northern terminus of this thunderstorm complex will end up, but there has been enough consistency in the most recent high-resolution model solutions to warrant the introduction of TEMPO groups for TSRA at the Chicago metro terminals and a PROB30 group for TSRA at RFD. That said, if several storms end up lighting up along the aforementioned surface boundary tonight, then that may increase the chances that this midday thunderstorm complex will end up passing south of the terminals later today.

Lastly, patchy MVFR ceilings are currently being observed in the area at press time, and it is possible that lower ceilings (possibly IFR or LIFR) could be observed later tonight through the early-mid morning. Fog/mist may develop in some areas as well and could also result in IFR or LIFR conditions being observed, especially at RFD, DPA, and GYY. Another episode of low ceilings and visibilities could occur early Thursday morning, and that potential will need to be assessed in greater detail for forthcoming TAF issuances.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.