000 FXUS63 KLOT 160805 AFDLOTArea Forecast Discussion National Weather Service Chicago/Romeoville, IL 305 AM CDT Tue Sep 16 2025
.KEY MESSAGES...
- Warm and dry conditions persist through the work week.
- Periodic shower and thunderstorm chances return this weekend into early next week (20-40%).
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.DISCUSSION... Issued at 305 AM CDT Tue Sep 16 2025
Expansive surface high pressure across the broader Great Lakes region early this morning has led to continued mostly clear skies and light and variable to calm winds. Radiational cooling across interior northern Illinois may lead to patchy shallow fog development through daybreak but coverage should remain much lower than seen over the weekend given overall drier low-levels.
A blocky upper-level flow pattern across the eastern CONUS will continue to support quiet weather conditions across our area through the work week. Mostly clear skies each day will foster unseasonably warm temperatures, with inland highs in the 80s to near 90 (warmest toward western and central Illinois) through the remainder of the work week. Closer to the lake, relatively weak surface flow will allow lake breezes to push inland each afternoon. This will thus result in cooler temperatures (mainly in the 70s) near the Lake Michigan lakeshore.
While quiet and dry weather will persist in this blocked pattern through the rest of the work week, the upper level ridge begins to break down heading into the weekend as a western trough (and/or potential cut-off low) begins to slide eastward towards the Great Lakes. This will lead to increasing chances for periodic showers and thunderstorms over the weekend into early next week.
Petr/KJB
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.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 1231 AM CDT Tue Sep 16 2025
No major forecast concerns are expected through the TAF period as high pressure remains overhead. Therefore, expect light and variable winds tonight to become east-northeast Tuesday morning with speeds in the 5-7 kt range. Skies will remain mostly clear through the period though some occasional passing cirrus is possible especially at RFD.
Finally, there is some shallow fog developing in far northeast IL and southern WI. Given the large temperature-dew point depressions (around 5-6 degrees) suspect fog will struggle to develop at the terminals and thus have forgone a formal mention. That said, did add a TEMPO at GYY for some 5SM BR given the low temp-dew point depression here and some fog being noted in Lake County, IN. Fog will erode after daybreak Tuesday morning.
Yack
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.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None.
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