555
FXUS63 KLOT 171827
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
127 PM CDT SAT OCT 17 2026
KEY MESSAGES
- FROST IS EXPECTED TONIGHT ACROSS NORTHWEST INDIANA AND
ESPECIALLY EAST OF I-55 IN ILLINOIS.
- AN EXTENDED PERIOD OF DRY AND UNSEASONABLY MILD WEATHER IS
EXPECTED THE UPCOMING WORK WEEK AND LIKELY INTO NEXT WEEKEND
AS WELL.
DISCUSSION
ISSUED AT 127 PM CDT SAT OCT 17 2026
FOLLOWING A CHILLY START TO THE DAY, SUNNY SKIES ARE BOOSTING
TEMPERATURES BACK THROUGH THE 50S EARLY THIS AFTERNOON.
MEANWHILE, LIGHT WINDS (~5 MPH OR LESS) TO NEARLY CALM
CONDITIONS PERSIST AS THE CENTER OF SURFACE HIGH PRESSURE SLIDES
EASTWARD INTO THE MID-MISSISSIPPI VALLEY. THIS LIGHT WIND REGIME
WILL CONTINUE TONIGHT UNDER CLEAR SKIES AS THE HIGH SHIFTS INTO
THE OHIO VALLEY. CONSEQUENTLY, ANOTHER CHILLY NIGHT IS EXPECTED
ACROSS THE AREA, PARTICULARLY AWAY FROM THE CHICAGO URBAN HEAT
ISLAND. OVERNIGHT LOWS ARE PROJECTED TO BOTTOM OUT IN THE LOW TO
MID-30S (40S IN THE CITY), WITH FROST FORMATION POSSIBLE ONCE
AGAIN.
NO CHANGES WERE MADE TO THE ONGOING FROST ADVISORY IN EFFECT
FOR AREAS GENERALLY EAST OF I-55, AS THIS REGION REMAINS THE
MOST FAVORED FOR CONTINUED NOCTURNAL DECOUPLING WITH LITTLE TO
NO SURFACE WIND THROUGH DAYBREAK SUNDAY MORNING. CONVERSELY,
AREAS NORTH OF THE ADVISORY AREA MAY SEE LIGHT SOUTHERLY WINDS
DEVELOP PRIOR TO DAYBREAK AS THE CENTER OF THE SURFACE HIGH
SHIFTS FURTHER EAST. ACCORDINGLY, WHILE TEMPERATURES WILL BE
COMPARABLE, SUBTLE BOUNDARY LAYER MIXING MAY BE SUFFICIENT TO
LIMIT WIDESPREAD FROST FORMATION OUTSIDE THE CURRENT ADVISORY
AREA.
FOLLOWING ANOTHER COOL MORNING, PLEASANT WEATHER IS EXPECTED
ACROSS THE REGION SUNDAY, THOUGH SOUTHWESTERLY WINDS WILL TURN
SLIGHTLY BREEZY BY THE AFTERNOON. AFTERNOON HIGHS SHOULD REBOUND
INTO THE LOW-TO-MID 60S UNDER MOSTLY SUNNY SKIES. THEREAFTER,
DRY AND UNSEASONABLY MILD WEATHER WILL PERSIST THROUGH THE
UPCOMING WEEK AS HIGH PRESSURE DOMINATES THE GREAT LAKES.
TEMPERATURES WILL TREND UPWARD INTO THE MID-TO-UPPER 60S ON
MONDAY, PEAKING IN THE LOW-TO-MID 70S (WARMEST INLAND) FROM
TUESDAY ONWARD. WHILE REMAINING BELOW RECORD THRESHOLDS (RECORD
HIGHS IN THE LOWER 80S AT CHICAGO AND ROCKFORD), THESE
TEMPERATURES ARE WELL ABOVE THE SEASONAL AVERAGE HIGH OF ~60
DEGREES.
KJB
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1217 PM CDT SAT OCT 17 2026
THERE ARE NO KEY CONCERNS TO HIGHLIGHT FOR THE 18Z TAF PERIOD.
SW WINDS BELOW 10 KT THROUGH THE NIGHT WILL GUST TO AROUND 20
KT FOR THE LATE MORNING AND AFTERNOON ON SUNDAY BEFORE SUBSIDING
FOR THE EVENING. EXPECT VFR WITH LARGELY CLEAR SKIES THROUGH
THE PERIOD.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...FROST ADVISORY FROM 3 AM TO 8 AM CDT SUNDAY FOR ILZ023-ILZ032-
ILZ033-ILZ039-ILZ108.
IN...FROST ADVISORY FROM 3 AM CDT /4 AM EDT/ TO 8 AM CDT /9 AM EDT/
SUNDAY FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR THE IL
AND IN NEARSHORE WATERS.
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