497
FXUS63 KLOT 170523
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1223 AM CDT WED SEP 17 2025
KEY MESSAGES
- PATCHY FOG IS EXPECTED EARLY THIS MORNING, SOME OF WHICH
COULD BECOME LOCALLY DENSE.
- WARM AND DRY CONDITIONS PERSIST THROUGH THE WORK WEEK.
- PERIODIC SHOWER AND THUNDERSTORM CHANCES RETURN THIS WEEKEND
INTO EARLY NEXT WEEK (20-40%).
DISCUSSION
ISSUED AT 233 PM CDT TUE SEP 16 2025
QUIET CONDITIONS WILL PERSIST THROUGH AT LEAST THURSDAY AS A
SOMEWHAT BLOCKED LARGE-SCALE PATTERN WITH A STRONG RIDGE OVER
THE GREAT LAKES BEGINS TO BREAK DOWN. CLOUD COVER WILL REMAIN
QUITE LOW WITH ONLY SOME CIRRUS FILTERING OVER THE AREA FROM A
PAIR OF UPPER-LEVEL LOWS SITUATED WELL TO THE WEST AND SOUTHEAST.
MEANWHILE, THE SOUTHWEST EXTENT OF A SURFACE RIDGE WILL REMAIN
ENTRENCHED OVER THE AREA THROUGH WEDNESDAY BEFORE ANOTHER RIDGE
NOSES SOUTHWARD TOWARD THE AREA ON THURSDAY. THIS WILL FAVOR AN
EXTENDED PERIOD OF GENERALLY E TO NE WINDS.
TEMPS WILL CONTINUE TO GRADUALLY WARM EACH DAY WITH INLAND
LOCATIONS EXPERIENCING HIGHS IN THE MID 80S AND LOWS IN THE MID
TO UPPER 50S. CLOSE TO THE LAKE, REINFORCEMENT OF LAKE-MODIFIED
AIR WILL RESULT IN HIGHS IN THE MID 70S AND LOWS IN THE 60S.
WHILE PRECIP IS UNLIKELY DURING THIS PERIOD, THE LONGER NIGHTS,
LIGHT WINDS, AND MOSTLY CLEAR SKIES COULD SUPPORT SHALLOW FOG
(PRIMARILY TONIGHT) GIVEN MARGINALLY FAVORABLE DEW POINTS IN
THE MID 50S. HAVE INCLUDED PATCHY FOG LATE TONIGHT THROUGH
SUNRISE FOR AREAS ALONG THE NORTH OF THE ILLINOIS RIVER AND
WEST OF THE I-294/94 CORRIDOR IN THE CHICAGO METRO.
KLUBER
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.
KJB
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1223 AM CDT WED SEP 17 2025
- MVFR VSBY REDUCTIONS IN BR EARLY THIS MORNING
THE COMBINATION OF CALM/VARIABLE WINDS, LOW-LEVEL MOISTURE DRIFTING
INLAND OFF LAKE MICHIGAN, AND RADIATIONAL COOLING UNDER CLEAR SKIES
MAY LEAD TO FOG DEVELOPMENT AGAIN EARLY THIS MORNING. IN CONTRAST TO
RECENT FOGGY MORNINGS IN THE SUBURBS, LOW-LEVEL MOISTURE MAY BE
SUFFICIENT FOR AT LEAST MVFR VSBY REDUCTIONS IN BR AT THE
CHICAGO TERMINALS (ORD/MDW). FOR NOW HAVE MAINTAINED MVFR TEMPOS
BUT HAVE NUDGED VSBYS DOWN TO 4SM (3SM AT DPA/GYY). THERE
REMAINS ABOUT A 5-10% CHANCE FOR NEAR LIFR VSBYS IN SOME SPOTS
TOWARD DAYBREAK AND OBSERVATIONAL TRENDS WILL BE MONITORED
CLOSELY.
WINDS RETURN TO A PREVAILING LIGHT NORTHEAST TO EAST DIRECTION
BEHIND A LAKE BREEZE LATE MORNING INTO THE AFTERNOON THEN EASE
AGAIN AFTER SUNSET. ANOTHER ROUND OF PATCHY FOG CAN'T BE RULED
OUT EARLY THURSDAY MORNING BUT WILL PLAN TO ADDRESS THAT WITH
LATER UPDATES IF CONFIDENCE INCREASES.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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