textproduct: Chicago

KEY MESSAGES

- Intermittent showers (and possibly a storm or two) are possible at times this morning.

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

DISCUSSION

Issued at 253 AM CDT Thu Aug 6 2026

A heavy rain producing MCS continues to mature across the lower Missouri Valley along the nose of a low-level jet early this morning. The remnants of this activity are expected to translate eastward, mostly south of our area, across central and southern IL around and shortly after daybreak this morning. In spite of this remaining to our south, we are not out of the woods from getting some showers and storms in parts of our area this morning. In fact, isolated to widely scattered showers have been festering over the past few hours, particularly south of I-88. This activity appears to be tied to a region of isentropic upglide (warm air advection) centered on the 305 K surface. The current thinking is that the modest warm air advection pattern will continue to support at least widely scattered showers as far north as the Chicago metro area for a few hours this morning. A few lightning strikes and brief heavy downpours may also accompany some of the stronger showers, but severe weather is not expected.

This morning shower activity looks to largely wane into this afternoon, though a few lingering showers cannot be ruled out, particularly to the south of I-80. However, cloud cover will persist this afternoon, making for a mostly cloudy day. Afternoon temperatures will hover in the mid and upper 70s to around 80 inland, with slightly cooler conditions favored closer to the lake due to a light onshore wind component.

Tonight, a small (20-30%) chance for a few additional isolated to widely scattered showers remain in the forecast, owing to the continued modest warm air advection pattern. However, outside of any showers, if any breaks in the cloud cover materialize, the light winds and very moist near surface conditions could set the stage for fog development into early Friday morning. I currently do not have a formal mention of fog in the forecast for tonight, largely due to uncertainties regarding cloud cover. Nevertheless, it will be something to monitor.

At this point, Friday is looking to be a largely dry day across our area as we remain between weather systems. Instead, the main focus for convection on Friday that we will be monitoring is a cold front, and accompanying mid-level impulse, which is forecast to shift eastward across the Upper Midwest during the day. As this front moves into our area Friday night, there is about a 20% that a few non-severe showers and storms could shift into our area, but the poor diurnal timing does not bode well for there being a good amount of coverage.

Saturday is expected to be mostly sunny and dry, but the weather pattern will shift quickly thereafter. As aggregate upper-level troughing moves east of the Great Lakes, subtropical ridging will become dominant across much of the southern CONUS. This transition will establish a seasonably strong west- northwesterly flow at mid and upper levels, extending from the Upper Midwest into the Great Lakes along the southern edge of a Hudson Bay Low. This setup is likely to trigger periodic waves of severe thunderstorms near a quasi-stationary surface frontal boundary, which is projected to stall over the lower Great Lakes region through early next week. While confidence in the precise timing and location of specific thunderstorm clusters remains low at this range, the overall pattern aligns with conceptual models for severe weather and flash flooding across the region from Sunday through at least early next week.

KJB

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 639 AM CDT Thu Aug 6 2026

Forecast concerns include...

Scattered showers through this afternoon. Mvfr cigs into this afternoon and possible again overnight. Chance of fog Friday morning.

Scattered showers will continue through this afternoon. There will likely be long breaks between the showers but there is quite a bit of uncertainty for timing and vicinity mention seems prudent through the afternoon. There may be an isolated thunderstorm today with the best chance and still low, mainly southeast of the terminals.

Cigs remain vfr this morning with guidance still showing mvfr cigs developing this morning and persisting into this afternoon before lifting and scattering. Maintained mvfr cigs with this forecast but confidence is decreasing. Mvfr cigs will be possible again overnight into Friday morning when there may also be a some fog. Confidence is too low to include either in this forecast.

Light and variable winds will slowly become light east/southeast this morning and likely remain southeasterly into this afternoon with light and variable winds expected tonight. Wind directions may favor more of a southwest direction by Friday morning. cms

LOT WATCHES/WARNINGS/ADVISORIES

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