textproduct: Chicago

KEY MESSAGES

- Active pattern looks to bring stormy weather to the region this weekend into early next week.

DISCUSSION

Issued at 201 PM CDT Thu Aug 6 2026

A weak shortwave trough continues to pivot across northeast IL and northwest IN this afternoon with a stalled frontal boundary hanging around the I-80 corridor. Despite these features, most areas have remained dry today aside from a cluster of showers traversing across IN. These showers will continue to move away from our area this afternoon. With the front expected to slowly meander south across the area this evening, additional isolated to widely scattered showers will likely continue to fester near and south of the front through this evening and possibly overnight as well. While thunder coverage should be low given the modest instability, occasional lightning strikes will be possible with any showers especially prior to sunset with about a 10-15% thunderstorm chance thereafter mainly for areas south of the Kankakee River Valley overnight.

Outside of the isolated showers, partly cloudy skies will linger through the night with temperatures cooling slightly into the mid to upper 60s. With more cloud cover forecast to hang around tonight, the threat for patchy fog is fairly low. However, with lingering low-level moisture and the light winds some patchy ground fog cannot be ruled out especially near the front and outside of the urban core of Chicago. Despite the lower confidence have opted to introduce some patchy (20% coverage) fog to the forecast for tonight.

Drier conditions are expected for Friday and Saturday as drier mid-level air advects in and puts a cap on the atmosphere. Skies should also scatter out through the day on Friday with mostly sunny skies for Friday afternoon and again on Saturday. Temperatures will be otherwise seasonable with highs in the mid-80s each day. However, there will be a low chance for a couple of lingering showers Friday morning in northwest IN followed by another low chance for scattered showers and storms Friday night as a front moves through. Given that the atmosphere should be capped the expectation is for any showers/storms to dissipate prior to reaching northern IL, but have maintained some 20-30% POPs just in case for now. The forecast for Saturday night onward generally remains unchanged as a strengthening upper ridge in the southwest CONUS will amplify the northwest flow over the Great Lakes. As a result, periods of thunderstorms are expected to traverse across the Great Lakes as several shortwaves dive through the region. The first period of interest will be late Saturday night into Sunday where guidance shows the first wave diving through. While guidance does show a complex of thunderstorms developing in the Upper Midwest and diving towards northern IL, there is a lot of variability as to whether or not the complex will track over us or miss us just to the west. Depending on where this complex goes will dictate how Sunday afternoon plays out locally which means we could get more scattered thunderstorms Sunday afternoon or stay dry until the next shortwave arrives on Monday. That said, the environment overhead Sunday afternoon will be one supportive of severe weather with strong instability and decent wind shear forecast to be present. Similarly, Monday afternoon also looks to be another period supportive of severe weather. Though confidence on storm timing and coverage Monday afternoon remains uncertain and will likely be dictated on how things evolve on Sunday. Bottom line, the end of the weekend and beginning of next week looks to start off active so make sure you keep checking back for forecast updates.

Additional periods of showers and thunderstorms will be possible through at least the middle of next week as the northwest flow remains in place. While there will be some dry hours mixed in, confidence on the specifics at this time range are low. Regardless, seasonable temperatures in the 80s (with overnight lows in the 60s) are forecast to prevail through the early part of next week.

Yack

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 644 PM CDT Thu Aug 6 2026

Winds are light southeast to southerly early this evening and are expected to gradually become light and variable after sunset. Winds then return to a prevailing SSW during the day on Friday around 5-10 kt.

While ceilings in the TAFs are currently VFR, there may be shorter periods of MVFR at times, including overnight outside of Chicago and potentially mid morning through early afternoon areawide. However, confidence in any particular TEMPO window for MVFR remains too low to include with this update.

Confidence in VSBY trends overnight into early Friday morning also remains on the lower side, though there continues to be a signal for east least MVFR VSBY reductions in BR outside of Chicago. Have nudged down VSBYs at RFD and DPA to 5SM for now. It does appear that there will be sufficient remnant cloud coverage to prevent more widespread VSBY reductions, though pockets of IFR or lower VSBYs certainly can't be ruled out and will need to be monitored for any shorter fused TAF updates through the night.

Have maintained a dry forecast with this update though a stray shower (VCSH) can't be fully ruled out tonight through Friday afternoon given the proximity of a stalled surface boundary near the area.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

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