177
FXUS63 KLOT 220831
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
331 AM CDT WED OCT 22 2025
KEY MESSAGES
- FROST ADVISORY IN EFFECT LATE TONIGHT INTO EARLY THURSDAY FOR
AREAS WEST/SOUTH OF THE CHICAGO METRO.
- BLUSTERY CONDITIONS CONTINUE TODAY, THOUGH WITH GRADUALLY
DECREASING WINDS.
- A MORE WIDESPREAD FROST IS LIKELY ACROSS MOST OF THE AREA
THURSDAY NIGHT INTO EARLY FRIDAY MORNING.
DISCUSSION
ISSUED AT 330 AM CDT WED OCT 22 2025
THROUGH THURSDAY:
HAVE ELECTED TO ISSUE A FROST ADVISORY FOR OUR WESTERN AND
SOUTHERN CWA COUNTIES OUTSIDE OF THE CHICAGO METRO AND NORTHWEST
IN FROM MIDNIGHT THROUGH 9 AM CDT THURSDAY MORNING. FROST LATE
TONIGHT/EARLY THURSDAY, GRADUALLY EASING WINDS AND SPOTTY
SHOWER TRENDS TODAY ARE THE MAIN FORECAST CONCERNS.
MAIN DRIVER OF OUR WEATHER CONDITIONS THROUGH THURSDAY
CONTINUES TO BE A BROAD UPPER LEVEL TROUGH ACROSS EASTERN NOAM
AND AN EMBEDDED CLOSED UPPER/SURFACE LOWS CURRENTLY CENTERED
OVER THE NORTHERN GREAT LAKES. WHILE THE UPPER LOW/OCCLUDING
SURFACE LOW WILL CONTINUE TO DRIFT TO THE EAST/NORTHEAST TODAY,
ADDITIONAL HIGHLY SHEARED MID-LEVEL VORT ENERGY CONTINUES TO
WRAP CYCLONICALLY SOUTHEASTWARD ACROSS THE REGION. THIS MAY
PRODUCE SOME SPOTTY LIGHT RAIN SHOWERS AT TIMES PARTICULARLY
EARLY THIS MORNING, AND AGAIN IN THE LATE AFTERNOON AND EARLY
EVENING HOURS PRIMARILY NORTHEAST OF THE I-90 CORRIDOR ACROSS
FAR NORTHEAST IL. A FEW OF THESE SHOWERS MAY ALSO CLIP PARTS OF
NORTHWEST IN, PARTICULARLY NORTHEAST PORTER COUNTY WHERE SOME
LAKE-EFFECT SHOWERS MAY ALSO LINGER INTO EARLY THURSDAY
MORNING, THOUGH LOW LEVEL WIND TRAJECTORIES FAVOR GREATER
CHANCES FARTHER EAST. EXTENSIVE CLOUD COVER THIS MORNING WILL
GRADUALLY DECREASE ACROSS OUR SOUTHWESTERN COUNTIES TODAY, AND
ACROSS THE REMAINDER OF THE AREA INTO THURSDAY.
BLUSTERY WEST TO WEST-NORTHWEST WINDS WILL PERSIST TODAY, WITH
GUSTS IN THE 30-35 MPH RANGE AT TIMES, THOUGH THESE WINDS
SHOULD GRADUALLY EASE WITH TIME LATER IN THE DAY. BETWEEN
PERSISTENT COLD ADVECTION AND CLOUD COVER, HIGHS SHOULD RANGE
FROM ONLY AROUND 50 FAR NORTHEAST, TO THE MID-50S IN THE
SOUTHWEST WHERE SOME SUNSHINE SHOULD DEVELOP THIS AFTERNOON.
DECREASING CLOUDINESS FROM THE SOUTHWEST TONIGHT IS EXPECTED TO
HELP WINDS DIMINISH, ALLOWING TEMPERATURES TO FALL INTO THE
LOWER 30S ROUGHLY SOUTHWEST OF A ROCKFORD TO KANKAKEE LINE AND
SETTING THE STAGE FOR WIDESPREAD FROST DEVELOPMENT THERE BY
SUNRISE THURSDAY MORNING. LINGERING CLOUD COVER, SLIGHTLY MORE
WIND AND THE EFFECTS OF THE WARMER CHICAGO METRO AND LAKE
MICHIGAN AREAS SHOULD KEEP THINGS WARMER THERE WITH
NORTHEASTWARD EXTENT. WITH THIS IN MIND, HAVE ISSUED A FROST
ADVISORY FROM MIDNIGHT TO 9 AM THURSDAY FOR MUCH OF THE
WEST/SOUTH PORTIONS OF THE AREA, BUT NOT FOR THE IMMEDIATE
CHICAGO AREA OR NORTHWEST INDIANA. SOME ADJUSTMENTS MAY BE
NEEDED BY THE DAY SHIFT IF ADDITIONS TO THE ADVISORY ARE NEEDED
FARTHER TO THE NORTHEAST/EAST.
THE CLOSED UPPER LOW AND OCCLUDED SURFACE LOW CONTINUE TO DRIFT
AWAY FROM THE AREA TO THE NORTHEAST ACROSS EASTERN ONTARIO AND
QUEBEC THURSDAY, ALLOWING FOR A CONTINUED DECREASE IN CLOUD
COVER, WINDS AND AND END TO SPOTTY SHOWERS IN NORTHWEST IN.
NORTHWEST FLOW WILL MAINTAIN COOL TEMPERATURES HOWEVER, WITH
HIGHS THURSDAY AGAIN IN THE 50S ACROSS THE AREA.
RATZER
THURSDAY NIGHT THROUGH TUESDAY:
SURFACE HIGH PRESSURE WILL SETTLE INTO THE REGION THURSDAY
NIGHT INTO FRIDAY AS UPPER-LEVEL LONGWAVE TROUGHING OVER THE
GREAT LAKES MAKES WAY FOR A LOW-AMPLITUDE UPPER-LEVEL RIDGE. THE
RESULTING CLEAR SKIES AND LIGHT/CALM WINDS WILL PROVIDE
CONDITIONS THAT WILL BE MORE OPTIMAL FOR RADIATIONAL COOLING AND
WIDESPREAD FROST DEVELOPMENT THURSDAY NIGHT COMPARED TO
TONIGHT/THURSDAY MORNING. THE NBM'S LOW TEMPERATURES FOR
THURSDAY NIGHT/FRIDAY MORNING HAVE MANY AREAS (PRIMARILY IN
INTERIOR NORTHERN ILLINOIS) FALLING BELOW FREEZING AS WELL,
THOUGH THE NBM'S LOW TEMPERATURES CONTINUE TO FALL ON THE
COLDER/LOWER END OF THE GUIDANCE ENVELOPE, LIKELY DUE TO THE
INFLUENCE OF THE COLD-BIASED AND OUTLYING CANADIAN GUIDANCE THAT
IS PART OF ITS MODEL INPUT. OPTED TO NUDGE THURSDAY NIGHT'S
LOWS A COUPLE OF DEGREES UPWARD TO BE CLOSER IN LINE WITH THE
EPS AND GEFS ENSEMBLE MEANS, BUT WITH BOTH ECMWF AND NCEP-BASED
GUIDANCE FAVORING DEW POINTS GETTING BELOW 32F IN SOME
LOCATIONS, THE DOOR CERTAINLY REMAINS OPEN FOR SUB-FREEZING
TEMPERATURES TO BE OBSERVED -- AT LEAST AT OUR USUAL OUTLYING
COOL SPOTS. CONFIDENCE IN WIDESPREAD BELOW FREEZING TEMPERATURES
BEING OBSERVED IN OUR CWA WAS TOO LOW AT THIS TIME TO GIVE
STRONG CONSIDERATION TO A ISSUING A FREEZE WATCH, BUT AT THE
VERY LEAST, ANOTHER FROST ADVISORY WILL ALMOST CERTAINLY BE
NEEDED FOR THURSDAY NIGHT/FRIDAY MORNING.
THE CONTINUED INFLUENCE OF HIGH PRESSURE/RIDGING WILL RESULT IN
FRIDAY BEING A DRY DAY ACROSS THE AREA WITH PLENTY OF SUNSHINE.
HOWEVER, THE COOL START TO THE DAY AND THE LOWER LATE OCTOBER
SUN ANGLE SHOULD CAUSE FRIDAY TO BE ANOTHER DAY WITH HIGHS IN
THE 50S ACROSS MOST, IF NOT ALL, OF OUR FORECAST AREA. ANOTHER
COOL NIGHT THEN LOOKS TO BE IN STORE FRIDAY NIGHT INTO SATURDAY
MORNING. THE NBM'S LOW TEMPERATURES FOR THIS PERIOD ALSO APPEAR
TO BE A BIT TOO COLD, THOUGH THEY AREN'T TOO FAR OFF THE
ENSEMBLE MEAN OF THE EPS, WHICH WOULD SUPPORT ANOTHER NIGHT OF
AT LEAST PATCHY FROST DEVELOPMENT, MAINLY IN AREAS OUTSIDE OF
THE CHICAGO METRO. HOWEVER, THE GEFS AND DETERMINISTIC GFS
REMAIN A BIT MILDER WITH LOW TEMPERATURES IN THE LOW-MID 40S
ACROSS A LARGE PORTION OF OUR FORECAST AREA, SO HAVE HELD OFF ON
INTRODUCING ANY NEW FROST MENTION FOR FRIDAY NIGHT/SATURDAY
MORNING INTO THE FORECAST GRIDS FOR NOW.
OVER THE WEEKEND, A NORTHERN STREAM UPPER-LEVEL SHORTWAVE AND A
CUT-OFF UPPER-LEVEL TROUGH FARTHER TO SOUTH WILL BOTH ATTEMPT
TO MAKE INROADS INTO THE REGION. MOST INDICATIONS IN ENSEMBLE
GUIDANCE NOW ARE THAT THE NORTHERN DISTURBANCE WILL END UP
TRACKING TO OUR NORTH, WHILE THE SOUTHERN DISTURBANCE TRACKS TO
OUR SOUTH OR SLOWS UP ENOUGH TO REMAIN AWAY FROM OUR AREA
THROUGH THE WEEKEND. THUS, A DRY WEEKEND APPEARS TO BE
INCREASINGLY LIKELY FOR THE AREA. GUIDANCE IS STILL IN GOOD
AGREEMENT ON THE GENERAL IDEA OF A MORE POTENT TROUGH EJECTING
INTO THE CENTRAL CONUS EARLY NEXT WEEK, THOUGH THERE IS STILL
UNSURPRISINGLY A VAST SPREAD IN ENSEMBLE GUIDANCE REGARDING ITS
EXACT EVOLUTION AND WHAT, IF ANY, INTERACTION IT WILL HAVE WITH
THE AFOREMENTIONED CUT-OFF TROUGH. MANY, BUT NOT ALL, ENSEMBLE
SOLUTIONS BRING QPF INTO OUR AREA SOMETIME IN THE EARLY-MID WEEK
TIME FRAME NEXT WEEK, SO THE CHANCE POPS OFFERED UP BY THE NBM
FOR THIS TIME FRAME REMAIN APPROPRIATE FOR NOW.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 101 AM CDT WED OCT 22 2025
KEY MESSAGES:
- WESTERLY WIND GUSTS IN THE 25-30 KT RANGE WILL CONTINUE
THROUGH EARLY THIS EVENING.
- MVFR CEILINGS ARE EXPECTED TONIGHT THROUGH MUCH OF THE
DAYTIME HOURS TODAY.
WHILE THE STRONGER WIND GUSTS MAY BECOME LESS FREQUENT DURING
THE OVERNIGHT HOURS, WESTERLY WINDS SHOULD OTHERWISE CONTINUE TO
GUST TO 25-30 KTS WITH REGULARITY THROUGH THE DAYTIME TODAY
BEFORE ABATING AFTER SUNSET. MVFR CEILINGS ARE ALSO SLOWLY
WORKING THEIR WAY SOUTHWARD FROM WISCONSIN AND SHOULD SETTLE IN
OVER THE TERMINALS PRIOR TO DAYBREAK. THESE CEILINGS WILL LIKELY
LINGER INTO THE AFTERNOON BEFORE GRADUALLY LIFTING AND
SCATTERING, ALLOWING FOR VFR CONDITIONS TO RETURN GOING INTO
THIS EVENING.
OGOREK
MARINE
ISSUED AT 330 AM CDT WED OCT 22 2025
LOW PRESSURE WILL CONTINUE TO SLOWLY DRIFT ACROSS AND EVENTUALLY
AWAY FROM THE NORTHERN GREAT LAKES REGION TODAY AND TONIGHT.
WESTERLY GALES WILL PERSIST INTO THIS MORNING, BUT SHOULD
EASE TO 30 KTS BY MIDDAY. WINDS WILL FURTHER EASE TO 20 TO 25
KTS BY THURSDAY.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM CDT THURSDAY FOR
ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-ILZ021-ILZ023-
ILZ032-ILZ033-ILZ039.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR WINTHROP
HARBOR IL TO GARY IN.
GALE WARNING UNTIL 9 AM CDT THIS MORNING FOR GARY TO BURNS
HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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