textproduct: Chicago

KEY MESSAGES

- A couple periods of showers and storms are expected in the general region through tonight. Repeated downpours may lead to localized flash flooding.

- Stormy conditions may return this weekend into early next week.

DISCUSSION

Issued at 248 AM CDT Wed Aug 5 2026

Broad aggregate mid and upper-level troughing over the north central CONUS will steer a few smaller scale impulses across our area, resulting in a few clusters of showers and thunderstorms across the region today into tonight. One such wave is currently driving a line of heavy rain producing showers and storms eastward across northern IL. Fortunately, the eastward movement ~25 mph is limiting the duration of heavy rainfall at any given location, thus limiting the flash flood threat, at least in the near term. Nevertheless, a quick localized inch of rain may fall under the strongest cores.

Following this initial line of showers and storms, we will be monitoring the trends with the ongoing cluster of storms over IA. A good amount of available guidance suggests that this activity will track eastward into northwestern IL around daybreak. Thereafter, it remains a bit unclear as to how long it may hold together as it moves into northeastern IL (especially north of I-80) during the mid-morning hours, owing to the poor diurnal timing and modest instability. Nevertheless, the current thinking is that there will at least be a region of weakening showers moving into the Chicago metro area (mainly in the 8-11 am timeframe). Should this activity hold together into northeastern IL this morning, the presence of deep rich moisture (precipitable water values nearly to 2") will support locally heavy downpours.

After a break in the shower activity this afternoon, another round of developing convection is probable near the surface frontal boundary late this afternoon and evening in response to the approach of the next mid-level impulse. However, with diurnal destabilization expected to remain limited across far northern IL (especially north of I-88 where temperatures will stay in the 70s) as a result of persistent cloud cover through the afternoon, the main focus for stronger convection will likely end up south of I-80. This thinking continues to match the SPC's current Day 1 outlook, which indicates a level 1 of 5 severe threat into west central IL. The main threat with any stronger storms would be locally strong damaging wind gusts and locally heavy rainfall, particularly associated with any strong storm clusters. The overall threat of flash flooding will ultimately be dependent upon if and where multiple storms to move over the same areas (training). While this possibility cannot be ruled out on a localized basis in parts of our area, the better potential for this may end up remaining south- southwest of our area.

The focus for active weather should largely shift south of the area for Thursday and Friday. However, active weather (with shower and thunderstorm chances) is likely to return eighter this weekend, or early next week.

KJB

Weekend onward:

As aggregate upper-level troughing shifts eastward toward the end of the week, a quasi-zonal to northwesterly upper-level flow pattern will materialize across the Upper Great Lakes region supporting additional waves of showers and storms. Some of these may be rambunctious as the eastern edge of an EML plume is repeatedly re-advected eastward atop a stalled frontal boundary draped across the Great Lakes. Naturally, confidence in when/where eventual thunderstorm clusters will roam is low at this range. With that said, the pattern matches conceptual models for threats for severe weather and flash flooding in the general region this weekend into early next week.

Borchardt/KJB

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 630 AM CDT Wed Aug 5 2026

Forecast concerns include...

Chance of thunderstorms, mainly this afternoon/evening. Low mvfr/ifr cigs along with fog overnight/Thursday morning. Wind directions overnight/Thursday morning.

Scattered showers will be possible for most of this morning, but thunderstorm chances continue to decrease and have removed thunder mention for all but RFD this morning and even there, chances are low. There may still be a lull in the showers from late morning through early afternoon and then there will be a better chance for thunderstorms mid/late this afternoon through mid evening. Confidence for this time period is only medium and some of the guidance has been trending south with the better coverage of thunderstorms later today. Opted to make no changes to the forecast for this time period though changes are possible as trends emerge later today. There will remain a chance for showers through the early overnight hours Thursday morning.

Light southerly winds currently will become more southwest this morning and more west/southwest this afternoon. Confidence is low for wind directions this evening through Thursday morning. If there is a broken line of thunderstorms moving across the terminals, winds will likely turn east/southeast behind them this evening and then possibly become light and variable overnight. A frontal boundary that was looking to stall across the terminals overnight, now appears it will stall northwest of the terminals, maintaining a light southerly wind overnight into Thursday morning.

This front will also serve as the focus for fog development, most likely just northwest of the area, possibly at RFD where tempo mention seems reasonable. For most of the area, low mvfr and possibly ifr cigs appear likely though only medium confidence. cms

LOT WATCHES/WARNINGS/ADVISORIES

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