013 FXUS63 KLOT 161739 AFDLOTArea Forecast Discussion National Weather Service Chicago/Romeoville, IL 1239 PM 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 /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1238 PM CDT Tue Sep 16 2025
VFR conditions are expected through much of the period as a surface high pressure ridge remains draped across the area. However, MVFR BR and/or MIFG are expected to develop at outlying sites (DPA, RFD, GYY) overnight. Higher surface moisture from lake-modified air may also support VFR BR at ORD late tonight through sunrise Wednesday.
Winds will settle ENE up to 10 knots this afternoon through this evening. Expect winds to become calm or light and VRB overnight, though the VRB winds may favor north or just west of north at ORD/MDW behind a weak land breeze. ENE winds up to 10 knots will resume by late Wednesday morning.
Kluber
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.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None.
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