441
FXUS63 KLOT 230828
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
328 AM CDT THU OCT 23 2025
KEY MESSAGES
- FREEZE WARNING HAS BEEN ISSUED FOR MUCH OF THE AREA AWAY FROM
THE LAKE AND CORE OF CHICAGO LATE TONIGHT INTO EARLY FRIDAY
MORNING. FROST ADVISORIES WILL BE IN EFFECT FOR SOUTHERN COOK
AND PORTER COUNTIES.
DISCUSSION
ISSUED AT 328 AM CDT THU OCT 23 2025
THROUGH FRIDAY:
FREEZE WARNING HAS BEEN ISSUED FOR MUCH OF THE AREA AWAY FROM
THE LAKE AND CORE OF CHICAGO LATE TONIGHT INTO EARLY FRIDAY
MORNING. FROST ADVISORIES WILL BE IN EFFECT FOR SOUTHERN COOK
AND PORTER COUNTIES.
TEMPERATURES HAVE FALLEN INTO THE LOW-MID 30S ACROSS WESTERN
AND SOUTHERN PORTIONS OF THE FORECAST AREA EARLY THIS MORNING.
WESTERLY WINDS LESS THAN 10 MPH AND PATCHY CLOUD COVER MAY KEEP
WIDESPREAD FROST FROM BEING TOO MUCH OF AN ISSUE IN SOME SPOTS
THIS MORNING, THOUGH WITH SEVERAL HOURS OF ADDITIONAL COOLING
AHEAD OF US WILL MAINTAIN THE CURRENT FROST ADVISORY WHICH
EXPIRES AT 9 AM THIS MORNING.
EARLY MORNING GOES VAPOR IMAGERY CONTINUES TO DEPICT A BROAD
UPPER TROUGH OVER EASTERN NORTH AMERICA, WITH A COMPLEX UPPER
LEVEL LOW WOBBLING ACROSS FAR EASTERN ONTARIO AND QUEBEC. THE
ASSOCIATED SURFACE LOW WAS WELL TO OUR NORTHEAST, LIFTING ACROSS
CENTRAL QUEBEC. LOCALLY, THE FORECAST AREA REMAINS IN A REGION
OF WEST-NORTHWESTERLY CYCLONIC FLOW ON THE SOUTHWESTERN
PERIPHERY OF THIS SYSTEM, RESULTING IN WEAK BUT PERSISTENT LOW-
LEVEL COLD/GRADUALLY DRIER ADVECTION. THIS HAS AND WILL CONTINUE
TO PRODUCE GRADUALLY DECREASING CLOUD COVER AND DIMINISHING
WEST-NORTHWEST WINDS ACROSS THE AREA TODAY. NO PRECIPITATION IS
EXPECTED, SAVE FOR A SLIGHT CHANCE (<20 PERCENT) OF A FEW LIGHT
LAKE-INDUCED SHOWERS CLIPPING FAR NORTHEAST PORTER COUNTY THIS
MORNING. OTHERWISE, PARTLY TO MOSTLY SUNNY CONDITIONS ARE
EXPECTED WITH TEMPERATURES IN THE 50S, AND NORTHWEST WINDS 10-15
MPH.
THE UPPER TROUGH WILL CONTINUE TO SHIFT SLOWLY OFF TO THE EAST
OF THE REGION TONIGHT, WITH RISING HEIGHTS/SUBSIDENCE RESULTING
IN SURFACE HIGH PRESSURE PUSHING ACROSS THE MISSISSIPPI VALLEY
AND INTO THE FORECAST AREA, WITH ~1026 MB SURFACE HIGH PROGGED
TO BE CENTERED OVER NORTHWEST IL BY FRIDAY MORNING. THIS WILL
ALLOW CLEARING SKIES AND LIGHT WINDS TO SET UP EXCELLENT
RADIATIVE COOLING CONDITIONS, ALLOWING OVERNIGHT TEMPERATURES
DROP TO/BELOW FREEZING INTO THE UPPER 20S AND LOW 30S IN MANY
PARTS OF THE CWA. THE EXCEPTION TO THIS WILL BE CLOSER TO THE
LAKE MICHIGAN SHORE AND THE CORE OF THE CITY OF CHICAGO WHERE
SOMEWHAT WARMER CONDITIONS ARE LIKELY, AS WELL AS NORTHERN
PORTER COUNTY WHERE A LITTLE MORE WIND OF THE LAKE SHOULD KEEP
FREEZING CONDITIONS FARTHER INLAND. BASED ON THESE EXPECTATIONS,
HAVE ELECTED TO ISSUE A FREEZE WARNING FOR MOST OF THE AREA
FROM 1 AM TO 8 AM FRIDAY MORNING. HAVE EXCLUDED CENTRAL AND
SOUTHERN COOK COUNTY AND PORTER COUNTY FROM THE WARNING FOR
ABOVE REASONS. HAVE ISSUED A FROST ADVISORY FOR SOUTHERN COOK
AND PORTER WITH SLIGHTLY MILDER TEMPS THERE, AND WILL HAVE NO
HEADLINE FOR CENTRAL COOK WHERE TEMPERATURES SHOULD REMAIN IN
THE MID-UPPER 30S.
THE SURFACE HIGH WILL DRIFT ACROSS THE AREA FRIDAY, EVENTUALLY
MOVING EAST OF THE AREA BY EVENING. PLENTY OF SUNSHINE IS
EXPECTED, WITH RELATIVELY LIGHT WINDS. THE COLD MORNING START
AND THE COOL AIR MASS WILL AGAIN LIMIT TEMPERATURES MAINLY TO
THE 50S, THOUGH FAR SOUTHERN PARTS OF THE FORECAST AREA COULD
TAG 60 DEGREES.
RATZER
FRIDAY NIGHT THROUGH WEDNESDAY:
THE CONTINUED INFLUENCE OF SURFACE HIGH PRESSURE SHOULD LEAD TO
ONE MORE CHILLY NIGHT FRIDAY INTO SATURDAY. WHILE WINDS WILL BE
LIGHT/CALM ONCE AGAIN OVERNIGHT, INCREASING MID-LEVEL AND HIGH-
LEVEL CLOUD COVER IN ADVANCE OF A PAIR OF UPPER-LEVEL
DISTURBANCES LOOKS LIKE IT COULD BE MORE OF A FACTOR FOR HOW LOW
TEMPERATURES WILL BE ABLE TO COOL. FOR THAT REASON, IT IS
LIKELY THAT LOW TEMPERATURES FRIDAY NIGHT/SATURDAY MORNING WILL
END UP BEING WARMER BY AT LEAST A FEW DEGREES IN MOST LOCATIONS
COMPARED TO TONIGHT/FRIDAY MORNING. STILL, MOST AVAILABLE MODEL
GUIDANCE FAVORS DEW POINTS REMAINING LOW ENOUGH TO SUPPORT
ANOTHER POTENTIAL FOR FROST AWAY FROM CHICAGO, COMMUNITIES ALONG
THE LAKE MICHIGAN SHORELINE, AND WHEREVER ANY THICKER CLOUD
COVER ENDS UP BEING OBSERVED. IN A SCENARIO WITH LESS CLOUD
COVER, SUB-FREEZING TEMPERATURES COULD BE IN PLAY ONCE AGAIN,
BUT LIKELY NOT TO THE SAME DEGREE AND SPATIAL EXTENT AS
TONIGHT/FRIDAY MORNING. GIVEN THE EXISTING UNCERTAINTIES, WILL
LET ANY FROST/FREEZE HEADLINE DECISIONS FOR THIS PERIOD BE MADE
IN FORTHCOMING FORECAST PACKAGES.
ENSEMBLE GUIDANCE CONTINUES TO EXHIBIT A RELATIVELY LARGE
SPREAD REGARDING THE TRACK AND EVOLUTION OF THE TWO
AFOREMENTIONED UPPER-LEVEL DISTURBANCES -- A COMPACT NORTHERN
STREAM SHORTWAVE DIVING SOUTHEASTWARD ACROSS THE UPPER MIDWEST
AND A SPRAWLING UPPER LOW TRACKING EASTWARD ACROSS THE
CENTRAL/SOUTHERN PLAINS. THE MAJORITY OF GRAND ENSEMBLE MEMBERS
DEPICT A SOLUTION THAT KEEPS MOST OR ALL OF OUR FORECAST AREA
DRY THROUGH THE WEEKEND, AND THAT IS REFLECTED IN THE LATEST NBM
POPS, WHICH LARGELY REMAIN AT OR BELOW 25% THROUGH SUNDAY
NIGHT. STILL, SEVERAL MEMBERS OF THE GEFS AND A SLIGHTLY GREATER
NUMBER OF EPS MEMBERS COMPARED TO 24 HOURS AGO OUTPUT QPF
SOMEWHERE IN OUR FORECAST AREA OVER THE WEEKEND (MAINLY ON
SUNDAY). THUS, WHILE A DRY WEEKEND WITH SEASONABLE TEMPERATURES
CURRENTLY REMAINS AS THE MOST LIKELY OUTCOME FOR MOST OF OUR
FORECAST AREA, IT'S NOT NECESSARILY A LOCK YET GIVEN THE
COMPLEXITY OF THE UPPER-LEVEL SYNOPTIC PATTERN EVOLUTION.
A MORE POTENT UPPER-LEVEL TROUGH IS THEN LIKELY TO EJECT INTO
THE CENTRAL CONUS EARLY NEXT WEEK. THE SPREAD AMONGST ENSEMBLE
GUIDANCE FOR HOW THIS TROUGH WILL EVOLVE AND WHAT IT WILL BRING
TO OUR AREA IN TERMS OF SENSIBLE WEATHER STILL REMAINS QUITE
VAST, IN NO SMALL PART DUE TO THE EXISTING UNCERTAINTIES
REGARDING THE PRECEDING DISTURBANCES. MANY ENSEMBLE SOLUTIONS
BRING WIDESPREAD RAINFALL INTO OUR AREA AS THIS TROUGH SWINGS
THROUGH THE REGION DURING THE EARLY TO MID-WEEK TIME FRAME,
WHILE OTHERS HAVE US LARGELY MISSING OUT ON PRECIPITATION
ALTOGETHER DURING THIS TIME FRAME, SO WILL CONTINUE TO ROLL
WITH THE BROAD-BRUSHED CHANCE POPS OFFERED UP BY THE NBM.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1239 AM CDT THU OCT 23 2025
THERE ARE NO SIGNIFICANT AVIATION FORECAST CONCERNS FOR THE
CURRENT TAF PERIOD.
WEST-NORTHWESTERLY GUSTS TO AROUND 20 KTS ARE EXPECTED TO OCCUR
WITH SOME REGULARITY FROM MID-MORNING THROUGH THIS AFTERNOON
BEFORE CEASING AT AROUND SUNSET. THERE IS UNCERTAINTY OVER HOW
QUICKLY THE FESTERING OVERNIGHT STRATOCUMULUS DECK NEAR/OVER THE
TERMINALS WILL ERODE AS IT IS NOT BEING HANDLED WELL AT ALL BY
FORECAST GUIDANCE. CLOUD BASES WITH THIS DECK ARE LIKELY TO
REMAIN ABOVE 3000 FT AGL, HOWEVER, AND VFR CONDITIONS ARE THUS
EXPECTED TO PREVAIL THROUGHOUT THE TAF PERIOD.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR ILZ003-ILZ004-
ILZ008-ILZ010-ILZ011-ILZ019-ILZ021-ILZ023-ILZ032-ILZ033-
ILZ039.
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 PM CDT THIS EVENING FOR GARY TO
BURNS HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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