806 FXUS63 KLOT 160531 AFDLOTArea Forecast Discussion National Weather Service Chicago/Romeoville, IL 1231 AM CDT Tue Sep 16 2025
.KEY MESSAGES...
- Warm and dry conditions persist through the work week.
- Periodic shower and thunderstorm chances return for the weekend (20-40%).
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.DISCUSSION... Issued at 136 PM CDT Mon Sep 15 2025
A blocky upper-level flow pattern, centered across the Great Lakes, will continue to support quiescent weather conditions across our area through the week. Accordingly, dry weather with 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 amidst expansive surface high pressure will favor daily inland drifting lake breezes. 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, this pattern will begin to break late in the week as a western trough (and/or potential cut- off low) begins to slide eastward towards the Great Lakes. The net result of this will be increasing chances for periodic showers and thunderstorms for this weekend into early next week. This will also be paired with cooler more seasonable temperatures in the 70s.
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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