097
FXUS63 KLOT 232314
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
614 PM CDT THU OCT 23 2025
KEY MESSAGES
- FREEZE WARNING IN EFFECT FROM LATE TONIGHT INTO EARLY FRIDAY
MORNING FOR MUCH OF THE AREA AWAY FROM THE LAKE AND CORE OF
CHICAGO. FROST ADVISORY IN EFFECT FOR SOUTHERN COOK AND
PORTER COUNTIES.
DISCUSSION
ISSUED AT 250 PM CDT THU OCT 23 2025
THROUGH FRIDAY NIGHT:
WITH NO NOTABLE CHANGES IN THINKING REGARDING THE OVERNIGHT
LOWS TONIGHT-EARLY FRIDAY, NO CHANGES WERE MADE TO THE EXISTING
FREEZE WARNING AND FROST ADVISORY HEADLINES IN EFFECT FROM 1 AM
TO 8 AM CDT FRIDAY. DEW POINT TEMPERATURES IN THE UPPER 20S TO
LOWER 30S AS OF THIS WRITING SHOULD TRANSLATE TO LOWS GENERALLY
IN THAT RANGE FOR LOCATIONS AWAY FROM THE LAKE (ESPECIALLY IN
SHORE) AND THE HEART OF THE CHICAGO URBAN HEAT ISLAND.
EXPANSIVE SURFACE HIGH PRESSURE OVERHEAD AND CLEAR SKIES WILL
SUPPORT EFFICIENT RADIATIONAL COOLING, EVEN WITH THE ONSET OF
MODEST WARM AIR ADVECTION ALOFT AFTER MIDNIGHT. WHILE RECENT MOS
GUIDANCE HAS BEEN RUNNING ABOVE SOME OF THE POINT FORECAST
LOWS, ESPECIALLY SOUTH OF I-80, TEMPERATURES IF ANYTHING EARLY
THIS (THURSDAY) MORNING WERE A BIT COOLER THAN FORECAST, SO
ULTIMATELY KEPT OUR GRIDDED FORECAST LOWS CLOSE TO THE PREVIOUS
ISSUANCE.
THE DRY AIR MASS AND FULL SUNSHINE WILL SUPPORT RECOVERY INTO
THE MID TO LOCALLY UPPER 50S (MILDEST FAR WEST AND SOUTHWEST
CWA) ON FRIDAY. SOME HIGH CLOUD COVER WILL FILTER IN LATE IN THE
DAY INTO FRIDAY NIGHT, RESULTING IN LOWS NOT QUITE AS COLD,
THOUGH FROST DEVELOPMENT WILL BE POSSIBLE AWAY FROM CHICAGO. IF
ENOUGH LOCATIONS OUTSIDE OF CHICAGO OBSERVE LOWS AT OR BELOW
32F EARLY FRIDAY, HOWEVER, THE DECISION MAY BE MADE ON THE DAY
SHIFT TO "END" THE GROWING SEASON (FOR FROST/FREEZE HEADLINE
PURPOSES).
SATURDAY THROUGH THURSDAY:
A DAMPENING MID-UPPER SHORT-WAVE TROUGH WILL TRACK SOUTHEAST
INTO THE MID-UPPER MS VALLEY ON SATURDAY AND THEN DRIFT OVERHEAD
SATURDAY NIGHT. THIS WILL BE RIGHT INTO THE ANTECEDENT DRY HIGH
PRESSURE PARKED OVER THE REGION. FOR THIS REASON (AND THE
DAMPENING NATURE OF THE SHORT-WAVE), RAIN MAY STRUGGLE TO REACH
THE GROUND, ESPECIALLY WITH NORTHEASTWARD EXTENT, AND COULD
VERY WELL BE LIMITED TO SPRINKLES (IF PRECIP REACHES THE
SURFACE). MOST OF THE LOW POPS (~20%) ARE CONFINED TO FAR
INTERIOR SECTIONS AND THEN ONCE OUT TO SUNDAY NIGHT, IT'S
POSSIBLE THAT THE GEFS SUITE IS TOO AGGRESSIVE WITH NORTHWARD
EXTENT OF RAIN WITH THE WEAK UPPER LOW WELL TO OUR SOUTHWEST. IF
THIS IS THE CASE, THE NEAR 30% POPS ALONG/SOUTH OF US-24 WILL
TREND DOWNWARD IN LATER UPDATES.
LOOKING AHEAD TO NEXT WORK WEEK, A COMPLEX MID-UPPER PATTERN
LENDS TO HIGHER UNCERTAINTY/LOWER CONFIDENCE REGARDING THE
EXTENT OF PRECIP CHANCES. A MORE POTENT UPPER TROUGH WILL DIVE
SOUTHEASTWARD AND RESULT IN A SURFACE LOW NEAR THE OHIO VALLEY.
BEFORE THIS SYSTEM PIVOTS FARTHER SOUTH AND EAST, IT'S
QUESTIONABLE IF ITS RAIN SHIELD WILL BE ABLE TO CLIP PARTS OF
OUR AREA OR IF THE PATTERN EVOLUTION AND ~1035 MB HIGH PRESSURE
REMAINING OVER QUEBEC WILL KEEP MOST IF NOT ALL OF THE RAIN
SUPPRESSED TO OUR SOUTH. THE TIMEFRAME OF INTEREST IS THE MONDAY
NIGHT INTO WEDNESDAY TIMEFRAME, WITH OUR POPS CURRENTLY PEAKING
IN THE 30-50% RANGE ADEQUATELY CAPTURING THE ENSEMBLE SPREAD
FOR NOW. IF MOST OF THE SYSTEM RAIN ENDS UP SOUTH, IT WILL BE
COOL ENOUGH ALOFT FOR LAKE EFFECT SHOWERS AT TIMES. IN ADDITION,
A PROLONGED PERIOD OF BRISK ONSHORE FLOW WILL SPELL BREEZY
DAYTIME CONDITIONS AND CHOPPY WAVES ON THE LAKE (FOR ANY BOATS
STILL VENTURING OUT).
CASTRO
AVIATION /00Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 614 PM CDT THU OCT 23 2025
NO MAJOR FORECAST CONCERNS FOR THIS TAF PERIOD AS A SURFACE HIGH
WILL BE MOVING OVERHEAD. THE ONGOING BREEZY NORTHWEST WINDS WILL
CONTINUE TO DIMINISH WITH SPEEDS FALLING TO 5 KTS OR LESS OVER
THE NEXT HOUR AND REMAINING AS SUCH THROUGH TONIGHT. SKIES WILL
REMAIN MOSTLY CLEAR OVERNIGHT WHICH WILL SET THE STAGE FOR
ANOTHER NIGHT OF FROST AND CHILLY TEMPERATURES AREAWIDE. FOR
FRIDAY, EXPECT NORTHWEST WINDS AROUND 5-8 KTS TO START THEN
BECOMING EASTERLY AFTER 21-22Z AS THE HIGH SLIDES THROUGH.
SPEEDS WILL ALSO DIMINISH TO AROUND 5 KTS AS WINDS CHANGE
DIRECTION. SKIES WILL REMAIN MOSTLY CLEAR THROUGH THE PERIOD, BUT
A PASSING 3500-4000 FT CUMULUS CLOUD CANNOT BE RULED OUT FRIDAY
AFTERNOON.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...FREEZE WARNING FROM 1 AM TO 8 AM CDT FRIDAY FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ106-
ILZ107-ILZ108.
FROST ADVISORY FROM 1 AM TO 8 AM CDT FRIDAY FOR ILZ105.
IN...FREEZE WARNING FROM 1 AM CDT /2 AM EDT/ TO 8 AM CDT /9 AM EDT/
FRIDAY FOR INZ001-INZ010-INZ011-INZ019.
FROST ADVISORY FROM 1 AM TO 8 AM CDT FRIDAY FOR INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 10 AM CDT FRIDAY FOR GARY TO BURNS
HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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