textproduct: Chicago

KEY MESSAGES

- Dry weather is expected through tonight, but thunderstorm chances return on Friday.

UPDATE

Issued at 837 PM CDT Wed Aug 19 2026

There were a few reports of funnel Clouds in Livingston, Ford, and Iroquois Counties this evening, but as sunset has passed, funnel cloud activity is not expected the rest of the night.

Generally, showers and storms have behaved in our area, with the focus more to the south and west of US-24. However, storm motions are very slow, around 5 to 10 mph to the southeast. Coverage is slowly expanding for areas south of the Kankakee River. A targeted area north of Cissna Park received 2 inches of rain in an hour on MRMS, and another appears to be developing southeast of Thawville. While coverage of the torrential rain is more isolated, given the already saturated soils a Flood Advisory was issued for southern Iroquois County. While storm motions are slow, the footprints of the heaviest rainfall rates have been quite small, lowering the confidence in the need for a Flash Flood Warning. That being said, we are also monitoring an axis of better coverage of rain moving into southern Livingston and eventually into Ford County where localized 1"+ per hour rain rates are being observed south of Pontiac.

DK

DISCUSSION

Issued at 233 PM CDT Wed Aug 19 2026

Through Tonight...

Showers and thunderstorms should tend to gradually weaken by mid evening as the area of showers/storms pushes gradually south of the area as diffuse front pushes slowly southward. Behind the front, skies will clear some tonight with light winds and still a fairly moist boundary would suggest that there could be some fog again late tonight into early Thursday morning. Best chance of clearing and light winds is over western CWA, so hit the fog the hardest in this area in the grids.

- Izzi

Thursday through Wednesday...

By early tomorrow, the stationary front and associated broad low pressure center will be moving away to the east making room for relative high pressure to slide over the region. The dry airmass will bring mostly sunny skies to tomorrow while afternoon temperatures look to peak in the upper 70s to near 80 degrees. The quiet pattern will be short-lived, however, as another trough axis is progged to swing across the Midwest late tomorrow night through Friday. A surface cold front will drop across the area on Friday bringing shower and thunderstorm chances.

Some pre-frontal activity will be possible in our northwest during the morning hours. Greatest chances will be during the afternoon and evening as the front works across. There is considerable uncertainty in the exact timing of the front and especially in the amount of instability that can build out ahead of it. Both will play a critical role in the potential strength of thunderstorms. The highly unstable solution from the NAM (4000+ J/kg of MLCAPE) seems unlikely as it's notably warmer at the surface and cooler aloft than other camps. But a couple to a few thousand Joules by the afternoon appear to be on the table. Shear is marginal at best, but that sort of instability would be supportive of potential severe weather with damaging winds and marginally severe hail being the primary concerns. Would like to think models should have a much better handle on the pre-frontal environment by tomorrow. The convection should largely be out of our area by the end of the evening.

On Saturday, the upper trough will strongly dig into the Great Lakes region and quickly spin up a center of surface low pressure to our east. It's possible that a few widely scattered showers develop on the backside of the system and fall on parts of the area during the day on Saturday, although the day should be largely dry with highs again forecast in the upper 70s to near 80. High pressure will then meander about the region early next week as seasonably warm conditions are favored to continue.

Doom

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1236 AM CDT Thu Aug 20 2026

High pressure building over the area will bring VFR conditions with periods of upper-level cloud cover throughout the forecast window. Light and sometimes VRB winds (but favoring NNE) are expected through mid-morning. ORD/MDW may see a brief period around sunrise when winds are just W of N (e.g. 340-000 degrees) at around 5 knots, but should return to E of N within an hour or two after sunrise. A lake breeze will then solidly shift winds NE around 10 knots late morning through the afternoon. Light and VRB winds around or less than 5 knots tonight will favor the SE quadrant in the evening and SW quadrant overnight into Friday morning.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...Flood Watch until 1 AM CDT early this morning for ILZ032- ILZ033-ILZ039.

IN...Flood Watch until 1 AM CDT /2 AM EDT/ early this morning for INZ010-INZ011-INZ019.

LM...None.