623
FXUS63 KLOT 170702
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
202 AM 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 /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1226 AM CDT SAT OCT 17 2026
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- PERIODS OF LAKE-EFFECT RAIN SHOWERS EXPECTED THROUGH 12Z
OVER NORTHWEST INDIANA
RECENT RADAR IMAGERY SHOWERS A STEADY STREAM OF LAKE-EFFECT
RAIN SHOWERS CONTINUING TO MOVE NORTH TO SOUTH OVER LAKE
MICHIGAN AND INTO NORTHWEST INDIANA. THIS ACTIVITY WILL CONTINUE
TO BRING PERIODS OF RAIN TO KGYY AND REGIONAL TERMINALS NEARBY
THROUGH DAYBREAK. A FEW SHOWERS MAY GET CLOSE TO THE EASTERN
SIDE OF MDW, BUT NO PRECIP IS EXPECTED THERE, JUST FEW/SCT
CLOUDS DUE TO PROXIMITY.
OTHERWISE, QUIETER VFR CONDITIONS ARE EXPECTED THROUGH THE TAF
WINDOW. WINDS CURRENTLY REMAIN OUT OF THE NORTH. THERE ARE A FEW
LINGERING SPOTS THAT FEATURE GUSTS TO 20 KNOTS, BUT THAT SHOULD
CONTINUE TO DIMINISH SHARPLY THROUGH THE OVERNIGHT. WINDS, 5 TO
10 KNOTS, WILL TURN TO THE SOUTHWEST THIS MORNING AND REMAIN
THERE THROUGH TOMORROW NIGHT. SUNDAY IS LOOKING A LITTLE
BREEZIER, BUT CURRENTLY OUTSIDE OF THE CURRENT TAF WINDOW.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...FREEZE WARNING FROM 5 AM TO 8 AM CDT THIS MORNING FOR ILZ003-
ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012.
FROST ADVISORY FROM 5 AM TO 8 AM CDT THIS MORNING FOR ILZ006-
ILZ019-ILZ020.
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 10 AM CDT THIS MORNING FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 3 PM CDT THIS AFTERNOON FOR THE IN
NEARSHORE WATERS.
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