000
FXUS63 KLOT 171717
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1217 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 202 AM CDT SAT OCT 17 2026
LAKE EFFECT SHOWERS ARE EXPECTED TO END EARLY THIS MORNING AS
INVERSION LOWER IN THE WAKE OF THE DEPARTING MID-UPPER LEVEL
TROUGH. LAKE CONVERGENCE BAND WILL GRADUALLY SHIFT WEST THIS
MORNING WITH LAKE EFFECT CLOUDINESS SPREADING INTO PORTIONS OF
NORTHEAST IL TOWARD SUNRISE. LAKE CLOUDINESS IS EXPECTED TO
DECREASE LATER THIS MORNING WITH SUNNY SKIES EXPECTED ELSEWHERE.
THE SUNSHINE AND MUCH LIGHTER WINDS WILL MAKE TODAY'S HIGHS IN
THE 50S FEEL MILDER THAN FRIDAY'S 50S.
EARLY THIS EVENING, HIGH PRESSURE WILL BE CENTERED OVER INDIANA
AND EASTERN IL. THE CLEAR SKIES, DRY BOUNDARY LAYER, AND
LIGHT/CALM WINDS SHOULD SET THE STAGE FOR STRONG RADIATIONAL
COOLING. THE HIGH PRESSURE SYSTEM IS PROGGED TO SHIFT SLOWLY
EAST TONIGHT, LIKELY ALLOWING A LIGHT SOUTH TO SOUTHWEST WIND TO
DEVELOP OVER NORTHERN CWA, WITH AREAS EAST OF I-55 INTO
NORTHWEST INDIANA PROBABLY REMAINING MORE DECOUPLED WITH LIGHT
OR NEARLY CALM WINDS UNTIL SUNRISE SUNDAY. HAVE SIDED WITH THE
SLIGHTLY CHILLIER MAV GUIDANCE FOR LOW TEMPS TONIGHT, WITH LOWS
IN THE 30S AWAY FROM THE URBAN HEAT ISLAND. THE COLDEST LOWS
SHOULD BE EAST OF I-55 AND IN THE TYPICALLY COLDER VALLEY AND
COLD AIR DRAINAGE AREAS OF NORTHERN IL WHERE LOWS IN THE LOW TO
MID 30S ARE EXPECTED.
THE MOST FAVORABLE AREA FOR FROST TONIGHT WILL BE EAST OF I-55
INTO NORTHWEST INDIANA AND AFTER COORDINATION WITH NEIGHBORING
WFOS, WE HAVE OPTED TO HOIST A FROST ADVISORY THERE. FARTHER
NORTH AND WEST, THERE ARE QUESTIONS ABOUT HOW WIDESPREAD FROST
WILL GET GIVEN THE INCREASING WINDS. PLUS, SOME OF THESE AREAS
MAY SEE AN END TO THE GROWING SEASON WITH FREEZING TEMPS THIS
MORNING. THE DAY SHIFT CAN TAKE A CLOSER LOOK AT THIS AND COULD
POTENTIALLY NEED TO EXPAND THE FROST ADVISORY A BIT FARTHER
NORTH/WEST.
OTHERWISE, THE WEATHER LOOKS INCREDIBLY TRANQUIL SUNDAY THROUGH
THE UPCOMING WORK WEEK. MANY OF THE DAYS ONE MAY BE HARD PRESSED
TO EVEN SPOT A CLOUD IN THE SKY! TEMPERATURES SUNDAY WILL
MODERATE BACK CLOSER TO NORMAL INTO THE LOW-MID 60S. MONDAY WILL
WARM A FEW MORE DEGREES, THEN BY TUESDAY THROUGH SATURDAY
AFTERNOON HIGHS ARE LARGELY EXPECTED TO BE IN THE 70S. THIS IS
PARTICULARLY IMPRESSIVE AT A TIME OF YEAR WHEN THE DAILY AVERAGE
HIGHS ARE FALLING QUITE QUICKLY. BY THE MIDDLE AND END OF THE
WEEK THE AVERAGE HIGHS ARE IN THE UPPER 50S, SO THE 70S WE'RE
FORECASTING WILL BE A GOOD 15-20F ABOVE AVERAGE!
- IZZI
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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