681 FXUS63 KLOT 161112 AFDLOTArea Forecast Discussion National Weather Service Chicago/Romeoville, IL 612 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 /12Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 612 AM CDT Tue Sep 16 2025
Patchy fog has developed across portions of far northern and northeast IL this morning with some localized visibilities down to a quarter mile. This fog will remain outside of the terminals and should begin to erode by 13-14z this morning. Otherwise, another tranquil forecast period is expected as high pressure remains in control overhead. Winds will become more east- northeast towards midday with speeds remaining in the 5-7 kt range before becoming light and variable again tonight. As for the skies, expect mostly clear conditions aside from a passing cirrus cloud.
Yack
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.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None.
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