textproduct: Chicago

KEY MESSAGES

- Isolated to widely scattered showers (and perhaps a few lightning strikes) are expected early this morning near Lake Michigan. If stronger showers develop and stall over areas that received torrential rain the past few days, a renewed flooding threat would occur. - Scattered showers and thunderstorms (20-40% chance) are expected this afternoon mainly near/south of I-80, but many areas will remain dry.

- Drier and more seasonable conditions are expected to start the week before stormier weather returns late week.

DISCUSSION

Issued at 253 AM CDT Sun Jul 5 2026

A baggy shortwave trough continues to reside over the western Great Lakes early this morning. Beneath the trough very saturated low-levels are keeping low stratus and fog across much of northern IL and northwest IN, with the worst of the fog over the Chicago metro and near Lake Michigan (basically areas that saw the heaviest rainfall yesterday). This fog is expected to linger through daybreak before eroding, but the threat for widespread dense fog appears to be waning.

The main forecast item of concern early this morning is whether or not more robust showers and perhaps an isolated storm will develop over the next several hours within the spotty showers already ongoing early this morning near Lake Michigan. While there is certainly enough moisture, the question is whether the forcing associated with the trough overhead and the broad surface low over southern Lake Michigan will be sufficient for more robust showers to develop. The main concern would be a threat for locally heavy rainfall due to the high moisture content and slow shower/storm motions which would lead to renewed flooding should these set up over the Chicago metro or anywhere that received heavy rain the past few days. With guidance not really handling the ongoing showers across the region, forecast confidence remains low. That said, have added some 20-30% POPs to the forecast near Lake Michigan through the morning to account for this potential and will continue to keep a close eye on radar trends.

Any showers (and/or storms) that develop early this morning will play a role on how things evolve this afternoon. If more widespread showers occur then the coverage of scattered showers and thunderstorms will likely be low and farther south. However, if the morning coverage is lower (which is the favored scenario) then a greater shower and thunderstorm coverage may materialize. With a lot of uncertainty on how this morning will play out, confidence on the coverage of afternoon showers/storms is also low. That said, with the aforementioned surface low expected to be traversing across lower MI later today, it seems the better environment for storms this afternoon will be near and south of the Kankakee River Valley (30-40% chance). As a precaution have included some 20-25% POPs as far north as I-80 in case things develop farther north but suspect most areas north of the Kankakee Valley should stay dry. Regardless of storm coverage, the limited wind shear and much weaker instability today should keep the severe threat virtually zero but a heavy rain threat will still exist with localized gusty winds up to 40 mph.

Otherwise, expect partly to mostly cloudy skies today with much cooler temperatures compared to the past few days. Highs today are only expected to top out in the lower 80s inland with those near the lake only expected to be in the mid to upper 70s due to the onshore winds. With winds expected to become a bit breezier this afternoon (speeds around 10-15 mph with gusts up to 20 mph) waves on the lake should increase into the 2 to 4 feet range this afternoon and evening. Though if winds verify a bit higher then some locally higher waves up to 5 feet could be seen. Bottom line, if you are heading to the beach today keep an eye on the waves and if they become too high for your comfort level then stay out of the water.

Heading into Monday, the trough overhead will be pivoting eastward and pushing the shower and storm chances east and south of our area. Temperatures on Monday will be on the seasonable side with highs in the lower to mid-80s inland with 70s expected near the lake due to persistent onshore winds. The dry weather will prevail into Tuesday, but with winds expected to be more southerly, temperatures should be a few degrees warmer with highs in the mid to upper 80s. However, the potential for a lake breeze Tuesday afternoon means that temperatures near the immediate lake shore will likely be a tad cooler in the upper 70s to lower 80s.

The upper level pattern is still forecast to become more west- southwesterly by Wednesday which will begin to advect in more humid air back into the region, though temperatures do look to stay more on the seasonable side with highs generally in the mid to upper 80s. With the increasing humidity will bring increasing chances for showers and thunderstorms for the latter half of the week and into next weekend. While confidence is decently high on the transition to another stormy pattern, the coverage and intensity of storms each day remains uncertain so be sure to check back for updates as we get closer.

Yack

AVIATION /06Z TAFS THROUGH 12Z MONDAY/

Issued at 0605 AM CDT Sun Jul 5 2026

Key aviation forecast messages:

- Gradual improvement from reduced VSBYs in FU/BR and low stratus through the early AM.

- 30% chance for SHRA early this morning through the afternoon.

- TS potential will be very spotty/isolated mid to late morning (if showers develop).

The combination of firework smoke and elevated humidity at the surface led to earlier IFR VSBYs at the Chicago area terminals. However, VSBYs have been gradually improving early this morning with the northern edge of the LIFR/IFR stratus already near DPA/ORD. The expectation is for CIG/VSBY trends to continue improve through the night, albeit slightly slower at MDW and GYY.

While confidence in development this far west remains low, there is a signal for isolated to widely scattered showers capable of heavy downpours over southern Lake Michigan and potentially into portions of the Chicago metro early this morning through midday. Account for this with PROB30s for SHRA that extend from ~10-17Z with a brief window where a few lightning strikes possible mid to late morning if the showers develop(covered by period VCTS from 14-17Z). Expect further adjustments based on radar and observational trends.

Winds will be generally north to northeast through the period with speeds increasing out of the east northeast during the daytime hours around 10-15 kt, highest near the lake.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Dense Fog Advisory until 9 AM CDT this morning for the IL nearshore waters.