763
FXUS63 KLOT 241124
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
524 AM CST WED DEC 24 2025
KEY MESSAGES
- THIS AFTERNOON THROUGH ALL OF CHRISTMAS DAY WILL BE GLOOMY AND
DECIDEDLY GRAY WITH NEARLY STAGNANT TEMPERATURES IN THE UPPER
30S (NORTH) TO LOWER 40S (SOUTH).
- PERIODS OF DRIZZLE, SHOWERS, AND DENSE FOG ARE EXPECTED (>80%
CHANCE) THIS EVENING THROUGH DAYBREAK THURSDAY/CHRISTMAS DAY.
- ANOTHER PERIOD OF DRIZZLE AND RAIN SHOWERS IS LIKELY (60 TO
80% CHANCE) THURSDAY NIGHT INTO FRIDAY.
- A RETURN TO MORE WINTER-LIKE CONDITIONS IS ON TRACK TO ARRIVE
NEXT WEEK. WIND CHILLS BELOW 0 MAY RETURN TO THE REGION AS
EARLY AS MONDAY MORNING, FOLLOWED BY A RETURN OF CHANCES FOR
SNOW BY MIDWEEK.
DISCUSSION
ISSUED AT 302 AM CST WED DEC 24 2025
TODAY THROUGH THURSDAY/CHRISTMAS DAY:
EARLY MORNING WATER VAPOR IMAGERY FROM GOES-16 AND GOES-17
DEPICT A HIGHLY AMPLIFIED PATTERN ACROSS THE UNITED STATES WITH
DEEP TROUGHING JUST OFFSHORE OF CALIFORNIA AND AN EXPANSIVE
RIDGE EXTENDING FROM THE FOUR CORNERS REGION TOWARD THE GREAT
LAKES. A BROAD REGION OF UPPER-LEVEL CLOUDS ARE STREAMING FROM
THE BASE OF THE TROUGH EASTWARD ACROSS THE RIDGE, AND INDEED
ACROSS OUR LOCAL AREA EARLY THIS MORNING. FOR THIS REASON, MANY
LOCATIONS HAVE PROBABLY ALREADY HIT OR ARE CLOSE TO THEIR
OVERNIGHT LOW FOR THIS MORNING. MEANWHILE, HAVE BEEN TRACKING A
SUBTLE RIPPLE PROPAGATING THROUGH THE BROADER ROSSBY WAVE EARLY
THIS MORNING (CURRENTLY CROSSING THE ROCKY MOUNTAINS AT PRESS
TIME). A LARGE AREA OF FOG AND STRATUS EXTENDING FROM CENTRAL
KANSAS THROUGH CENTRAL MISSOURI HAS STARTED TO PIVOT
NORTHEASTWARD IN ADVANCE OF THE APPROACHING UPPER-LEVEL RIPPLE,
ALIGNING ON A TRAJECTORY TO MOVE ACROSS OUR AREA LATER TODAY.
FIRST THING IS FIRST. AFTER SUNRISE, AT LEAST SOME MIXING INTO
THE BASE OF THE STRONG LOW-LEVEL INVERSION SHOULD ALLOW FOR
SURFACE TEMPERATURES TO RISE INTO THE LOW TO MID 40S. HAVE
NOTED HRRR/RAP GUIDANCE SHOWING AREAS EAST OF I-55 MAKE A RUN
FOR THE LOWER 50S BY EARLY AFTERNOON, THOUGH AM NOT QUITE READY
TO BITE GIVEN THE EXPECTATION FOR OVERCAST SKIES THROUGH THE
MORNING HOURS (WHICH SHOULD TEND TO LIMIT BOTH DIURNAL HEATING
AS WELL AS MIXING DEPTHS). BY EARLY AFTERNOON, THE
AFOREMENTIONED PLUME OF FOG AND LOW-LEVEL STRATUS WILL ARRIVE
FROM THE SOUTHWEST AND DEEPEN OWING TO LIFT FACILITATED BY THE
INCOMING UPPER-LEVEL WAVE. HIGH RESOLUTION AND GLOBAL ENSEMBLE
SYSTEMS AS WELL AS FORECAST MODEL SOUNDINGS FROM DETERMINISTIC
COUNTERPARTS REMAIN IN EXCELLENT AGREEMENT THAT THE STRATUS
WILL GROW SUFFICIENTLY DEEP AND IN-CLOUD SHEAR WILL BECOME
SUPPORTIVE OF THE COALITION-COALESCENCE PROCESS, ALTOGETHER
AFFORDING WIDESPREAD DRIZZLE ACROSS OUR AREA THIS EVENING. AS A
RESULT, FELT COMFORTABLE DRAWING IN "DEFINITE" 80% POPS FOR
DRIZZLE EXPANDING FROM SOUTHWEST TO NORTHEAST ACROSS OUR AREA
THIS EVENING. (JUST HAVE TO NOTE, HAVE BEEN VERY IMPRESSED WITH
ENSEMBLE GUIDANCE DEPICTING SUCH A CONSISTENT SIGNAL FOR DRIZZLE
FOR THIS EVENING SINCE AT LEAST DECEMBER 18, CONSIDERING THE
RESPONSIBLE WAVE IS SO SUBTLE).
EVEN AS FORCING TIED TO THE UPPER-LEVEL RIPPLE DEPARTS TO THE
EAST BEFORE MIDNIGHT, A CONTINUATION OF MODEST IN-CLOUD SHEAR
WITHIN THE DEEP STRATUS LAYER SUGGESTS DRIZZLE MAY CONTINUE
THROUGH MUCH OF THE OVERNIGHT HOURS, ESPECIALLY WITH SOUTHWARD
EXTENT. SO, FELT THE COURSE OF LEAST REGRET WAS TO ONLY
GRADUALLY DECREASE POPS THROUGH THE NIGHT, MORE OR LESS CARRYING
DRIZZLE IN THE FORECAST ACROSS THE AREA ALL THE WAY THROUGH
DAYBREAK THURSDAY. NOW, WHEN AND WHERE DRIZZLE DOES END, LIGHT
SURFACE WINDS AND TRAPPED LOW-LEVEL MOISTURE BENEATH THE
INVERSION WILL BE SUPPORTIVE OF DENSE FOG. WITH MODESTLY
INCREASING NORTHEASTERLY FLOW ON THE SOUTHERN SIDE OF A CANADIAN
HIGH PRESSURE SYSTEM SETTLING IN THE UPPER GREAT LAKES TOWARD
DAYBREAK, THE SIGNAL FOR DENSE FOG IN MODEL GUIDANCE IS
CURRENTLY HIGHEST NEAR AND SOUTH OF I-80. SO, WILL FEATURE AREAS
OF FOG IN OUR GRIDDED DATABASE SOUTH OF I-80 AND PATCHY FOG
ELSEWHERE. RUDOLPH BETTER GRAB A PAIR OF FOG LIGHTS SINCE HIS
RED NOSE MAY NOT CUT IT TONIGHT.
ANY FOG AFTER DAYBREAK CHRISTMAS MORNING IS CURRENTLY FAVORED
TO SHIFT SOUTHWARD AS NORTH TO NORTHEASTERLY FLOW INCREASES OFF
LAKE MICHIGAN. HAVE NOTED A SUBTLE SIGNAL IN RAP GUIDANCE FOR
FOG TO DEVELOP OVER LAKE MICHIGAN AND ADVECT INLAND ACROSS
NORTHEASTERN ILLINOIS DURING THE MORNING HOURS, WHICH SEEMS
PLAUSIBLY GIVEN FORECAST DEW POINTS WILL BE CLOSE TO WATER
TEMPERATURES. FOR NOW, WILL KEEP ANY MARINE FOG OUT OF THE
FORECAST, BUT THIS WILL BE SOMETHING TO KEEP AN EYE ON.
CHRISTMAS DAY IS OTHERWISE SHAPING UP TO BE MORE OF THE SAME
WITH CLOUDY SKIES AND TEMPERATURES IN THE UPPER 30S (NORTH) TO
LOWER 40S (SOUTH).
ONE LAST THING, AND MORE OF A NICHE "GEE WIZ" STAT. THE
DIFFERENCE BETWEEN THE FORECAST HIGH AND LOW TEMPERATURES ON
CHRISTMAS DAY AT CHICAGO O'HARE IS ONLY 3 DEGREES. SHOULD OUR
FORECAST VERIFY EXACTLY, CHRISTMAS 2025 WOULD JOIN JUST FIVE
OTHER CHRISTMASES DURING WHICH THE DIFFERENCE FROM THE HIGH AND
LOW TEMPERATURES WAS 3 OR FEWER DEGREES: 1898 (3 DEGREES) 1934
(3 DEGREES), 1942 (3 DEGREES), 1956 (2 DEGREES), AND 2005 (3
DEGREES). IF THE TEMPERATURE RANGE BETWEEN THE HIGH AND LOW IS
INCREASED TO 4, THE LIST GETS LONGER BY 5 DATES. SO, WE'RE
REALLY SLICING THE ONION THIN. THE FORECAST DIFFERENCE IN HIGHS
AND LOWS AT ROCKFORD FOR THIS CHRISTMAS OF 5 DEGREES, WHICH IS A
BIT EASIER TO ACHIEVE AND HENCE MORE PREVALENT IN THE CLIMATE
DATABASE.
BORCHARDT
THURSDAY/CHRISTMAS NIGHT THROUGH NEXT WEDNESDAY:
MODEST MID-LEVEL RIDGING WILL BE PROGRESSING EASTWARD AS A PAIR
OF PACIFIC SHORTWAVE TROUGHS (ONE TRAVERSING ACROSS SOUTHERN
CANADA AND THE NORTHERN GREAT LAKES AND THE OTHER EJECTING OUT
OF THE CENTRAL PLAINS) APPROACH OUR AREA THURSDAY EVENING. AT
THE SURFACE, THE BAROCLINIC ZONE WILL STILL BE RESIDING IN
CENTRAL IL, BUT WILL BEGIN TO LIFT NORTHWARD AS THE PLAINS
SHORTWAVE AND ITS ASSOCIATED SURFACE LOW MOVES INTO THE
MISSISSIPPI VALLEY AND SOUTHERN GREAT LAKES. AS THIS OCCURS, A
BAND OF LIGHT RAIN AND DRIZZLE IS EXPECTED TO DEVELOP ALONG THE
SURGING WARM FRONT THURSDAY NIGHT AND TRANSITION INTO A MORE
BONAFIDE RAIN FRIDAY MORNING AS MORE ROBUST MOISTURE ARRIVES.
DUE TO THE PROGRESSIVE NATURE OF THE RAIN, IT SEEMS THAT AMOUNTS
WILL BE SOMEWHERE IN THE 0.10-0.15 INCH RANGE AND THUS NO
FLOODING CONCERNS ARE EXPECTED. HOWEVER, FORECAST SOUNDINGS
CONTINUE TO SHOW SOME FAIRLY STEEP LAPSE RATES(AROUND
7.0C/KM) WHICH STILL MAY RESULT IN SOME LOCALIZED HIGHER RAIN
AMOUNTS AND ISOLATED RUMBLES OF THUNDER. THAT SAID, WITH DEW
POINTS STILL FORECAST TO BE IN THE 40S TO NEAR 50F (WHICH WILL
LIMIT OVERALL BUOYANCY) ON FRIDAY CONFIDENCE ON THUNDER REMAINS
LOW AND THUS HAVE FOREGONE A FORMAL MENTION IN THE FORECAST.
WITH THE AFOREMENTIONED BAROCLINIC ZONE LIFTING THROUGH THE
AREA, TEMPERATURES ON FRIDAY WILL LIKELY VARY FROM NORTH TO
SOUTH. SO, EXPECT HIGHS ON FRIDAY TO BE GENERALLY IN THE
MID-40S NORTH OF I-80 WHILE THOSE TO THE SOUTH SEE VALUES CLOSER
TO THE UPPER 40S AND LOWER 50S PARTICULARLY SOUTH OF THE
KANKAKEE RIVER. HOWEVER, IT SHOULD BE NOTED THAT CLOUDS, RAIN,
AND NORTHWEST WINDS COULD STILL KEEP TEMPERATURES A DEGREE OR
TWO COLDER ESPECIALLY IF THE BAROCLINIC ZONE STRUGGLES TO LIFT
NORTHWARD.
A SURFACE HIGH AND ASSOCIATED MID-LEVEL RIDGING IS FORECAST TO
PIVOT OVER NORTHERN IL AND NORTHWEST IN FRIDAY NIGHT AND ALLOW
THE RAIN TO CONCLUDE. THOUGH, LINGERING LOW-LEVEL MOISTURE DOES
LOOK TO KEEP SKIES MOSTLY TO COMPLETELY CLOUDY THROUGH SATURDAY.
IN ADDITION, THE BAROCLINIC ZONE IS FORECAST TO STILL BE
HOVERING IN THE AREA (MOST LIKELY NEAR THE I-80 CORRIDOR) WHICH
WILL SET UP ANOTHER MILD DAY WITH HIGHS SIMILAR TO FRIDAY
(MID-40S NORTH AND UPPER 40S TO LOW 50S SOUTH). ALTHOUGH IF THE
BAROCLINIC ZONE IS ABLE TO WOBBLE A BIT FURTHER NORTH THEN
SLIGHTLY WARMER TEMPERATURES (HIGHS IN THE MID-50S) COULD SNEAK
INTO AREAS SOUTH OF THE KANKAKEE RIVER.
THE TAIL END OF THE WEEKEND AND EARLY PART OF NEXT WEEK
CONTINUE TO LOOK ACTIVE AS THE LONGWAVE TROUGH THAT HAS BEEN
PARKED OVER THE PACIFIC NORTHWEST THE PAST SEVERAL DAYS IS
FORECAST TO BREAK LOSE AND EJECT EASTWARD ON SATURDAY. AS IT
DOES SO, IT IS EXPECTED TO PHASE WITH A DEEPENING SHORTWAVE
TROUGH OVER THE CANADIAN PRAIRIE PROVINCES AND NORTHERN PLAINS
WHICH IN TURN WILL ALLOW A SURFACE LOW TO DEVELOP OVER ONTARIO.
ATTACHED TO THIS LOW IS EXPECTED TO BE A COLD FRONT THAT LOOKS
TO BE DRAPED ACROSS THE UPPER MIDWEST TO CENTRAL PLAINS SATURDAY
AFTERNOON. THE COLD FRONT WILL THEN BEGIN TO RACE EASTWARD
THROUGH OUR AREA AND THE REST OF THE GREAT LAKES SATURDAY NIGHT
INTO SUNDAY. WHILE GUIDANCE CONTINUES TO SHOW A SECONDARY
SURFACE LOW DEVELOPING NEAR MO AND THE OHIO RIVER VALLEY, IT
SEEMS THAT SUFFICIENT MOISTURE SHOULD BE ABLE OOZE INTO NORTHERN
IL AND NORTHWEST IN AND GENERATE SOME LIGHT RAIN AND/OR DRIZZLE
AHEAD OF THE COLD FRONT SATURDAY NIGHT. GIVEN THE LIGHT NATURE
OF THE RAIN/DRIZZLE, NBM CONTINUES TO BE SOMEWHAT LOW ON POPS
(AROUND 15-20%), BUT WITH SOME UNCERTAINTY AS TO COVERAGE OF
RAIN/DRIZZLE LOCALLY, HAVE OPTED TO LEAVE POPS AS IS FOR NOW.
BUT SUSPECT WE WILL NEED TO INCREASE THEM IF THE FORECAST
CONTINUES TO TREND WETTER.
IN THE WAKE OF THE COLD FRONT, TEMPERATURES ARE EXPECTED TO BE
TANKING SATURDAY NIGHT AND THROUGH THE DAY ON SUNDAY. SINCE THE
GENERAL CONSENSUS AMONG ENSEMBLE MEMBERS IS TO HAVE THE HIGH
TEMPERATURE ON SUNDAY OCCUR NEAR MIDNIGHT SATURDAY NIGHT, THE
OFFERED NBM TEMPERATURES ARE LIKELY WAY TOO WARM. WHILE SOME
ADJUSTMENT WAS DONE TO TRY AND BETTER REFLECT THE NON-DIURNAL
TREND IN TEMPERATURES, FURTHER REFINEMENT WILL BE NEED WITH
FUTURE FORECAST CYCLES SO EXPECT TEMPERATURES DURING THE DAY ON
SUNDAY TO ONLY BE IN THE MID TO MAYBE UPPER 30S, AT BEST. AS
FOR PRECIPITATION, THE COOLING TEMPERATURES BEHIND THE FRONT
SATURDAY NIGHT INTO SUNDAY WILL TRANSITION ANY RAIN/DRIZZLE OVER
TO SNOW AND FLURRIES. HOWEVER, WITH DRIER AIR EXPECTED TO BE
FILTERING IN BY SUNDAY AFTERNOON IT SEEMS THAT SNOW QUALITY MAY
BE SOMEWHAT POOR WHICH SHOULD FAVOR MORE FLURRIES WITH LIMITED
ACCUMULATION AS OPPOSED TO TRUE SNOW SHOWERS.
ADDITIONALLY, THE STRONG COLD ADVECTION AND TIGHT PRESSURE
GRADIENT GENERATED BY THE SUB 1000 MB LOW IN THE NORTHERN GREAT
LAKES WILL LEAD TO BLUSTERY NORTHWEST WINDS GUSTING 25-35 MPH
(PERHAPS EVEN 40 TO 45 MPH) ON SUNDAY INTO THE DAY ON MONDAY.
WITH OVERNIGHT LOWS SUNDAY NIGHT FORECAST TO DIP NEAR THE LOWER
TEENS TO SINGLE DIGITS, THERE LOOKS TO BE A PERIOD OF SUB-ZERO
WIND CHILLS TO START OFF MONDAY MORNING. DESPITE TEMPERATURES
FORECAST TO REBOUND INTO THE 20S ON MONDAY, THE BLUSTERY WINDS
LOOK TO KEEP SINGLE DIGIT WIND CHILLS IN PLAY.
BEYOND MONDAY THE FORECAST CONTINUES TO BE RATHER UNCERTAIN DUE
TO A SHIFT IN THE UPPER PATTERN. WHILE THERE SEEMS TO BE
CONVERGING SIGNAL FOR A BRIEF WARMING PERIOD FOR TUESDAY AND
POSSIBLY WEDNESDAY (HIGHS FORECAST IN THE 30S), PERSISTENT
TROUGHING IS FAVORED TO SETTLE OVER THE GREAT LAKES AND EASTERN
CONUS TOWARDS THE LATER HALF OF NEXT WEEK (WEDNESDAY TO FRIDAY
TIMEFRAME). DEPENDING ON HOW THE TROUGHING SETS UP, IT LOOKS AS
IF NORTHERN IL AND NORTHWEST IN COULD GET BENEATH A NORTHWEST
FLOW PATTERN WHICH WOULD FAVOR MORE CLIPPER TYPE SYSTEMS AND THE
RETURN OF MUCH COLDER AIR TO THE AREA. THE OVERALL ENSEMBLE
SEEMS TO BE IN DECENT AGREEMENT ON THE COLD, BUT VARIES ON
WHETHER OR NOT OUR AREA WILL SEE ANY CLIPPERS AND IF SO WHEN
EXACTLY. THAT SAID, THERE DOES SEEM TO BE A SIGNAL FOR SOME
WINTRY WEATHER IN AT LEAST THE GENERAL REGION AROUND NEW YEARS,
SO IF YOU HAVE ANY PLANS RECOMMEND KEEPING A CLOSE EYE ON THE
FORECAST GOING FORWARD.
YACK
AVIATION /12Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 524 AM CST WED DEC 24 2025
FORECAST CONCERNS FOR THE TERMINALS...
- PERIOD OF LIGHT RAIN AND DRIZZLE THIS AFTERNOON AND EVENING,
BECOMING PATCHY FOG OVERNIGHT RESULTING IN MVFR VISIBILITIES.
- CEILINGS LOWERING TO MVFR THIS EVENING AND THEN TO IFR
OVERNIGHT ESPECIALLY AT THE CHICAGO AREA TERMINALS. CEILINGS
TO IMPROVE TO MVFR THURSDAY MORNING.
A SURFACE HIGH CONTINUES TO SWING THROUGH THE GREAT LAKES REGION
THIS MORNING WHICH IS GENERATING THE LIGHT EAST-NORTHEAST WINDS.
WHILE THERE IS SOME PATCHY FOG IN CENTRAL IL AND IN, THIS FOG
WILL REMAIN WELL SOUTH AND EAST OF THE TERMINALS BEFORE
DISSIPATING AFTER DAYBREAK. OTHERWISE, EXPECT BKN VFR CIRRUS TO
REMAIN OVERHEAD THROUGH THE MORNING WITH WINDS INCREASING AND
BECOMING MORE SOUTHEAST BY MID-MORNING.
HEADING INTO THIS AFTERNOON, THE WARM FRONT AND ITS ASSOCIATED
UPPER DISTURBANCE NEAR THE OHIO RIVER WILL BEGIN TO LIFT INTO
NORTHERN IL AND NORTHWEST IN. AS THIS OCCURS, LIGHT RAIN AND
DRIZZLE IS EXPECTED TO DEVELOP ALONG THE FRONT AND SPREAD OVER
THE TERMINALS BETWEEN 22Z AND 00Z THIS EVENING. ONCE
RAIN/DRIZZLE ARRIVES IT WILL PERSIST THROUGH MOST OF THE NIGHT
BEFORE TRANSITIONING TO PATCHY FOG AFTER MIDNIGHT AS MOISTURE
DEPTHS DIMINISH. WHILE VISIBILITIES WITH THE DRIZZLE AND FOG ARE
GENERALLY EXPECTED TO BE MVFR AT THE TAF SITES, LOWER
VISIBILITIES ARE EXPECTED TO DEVELOP NEAR THE WARM FRONT IN
CENTRAL IL AND COULD GET AS FAR NORTH AS GYY. SINCE THE COVERAGE
OF IFR OR LOWER VISIBILITY IS LOWER CONFIDENCE, HAVE OPTED TO
HANDLE WITH A TEMPO AT GYY FOR NOW.
ADDITIONALLY, CEILINGS WILL ALSO BE LOWERING AS THE RAIN/DRIZZLE
ARRIVES. MVFR CEILINGS SHOULD LARGELY PREVAIL THROUGH THE
EVENING, BUT AS THE WARM FRONT NEARS THE I-80 CORRIDOR IT SEEMS
SOME IFR CEILINGS WILL MATERIALIZE AT THE CHICAGO AREA TERMINALS
AFTER MIDNIGHT. DESPITE GUIDANCE STARTING TO TREND AWAY FROM
THE IFR WITHIN RECENT RUNS, THE CONCEPTUAL MODEL OF LOWER
CEILINGS NEAR THE WARM FRONT STILL MAKES CONFIDENCE HIGH ENOUGH
TO WARRANT MAINTAINING IFR CEILINGS IN THE TAFS. REGARDLESS, ANY
FOG AND IFR OVERNIGHT WILL GRADUALLY DIMINISH TOWARDS DAYBREAK
ON THURSDAY AS WINDS INCREASE AND TURN NORTHEASTERLY. HOWEVER,
MVFR CEILINGS WILL LINGER THROUGH THE END OF THE TAF PERIOD.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 9 AM THURSDAY TO NOON CST FRIDAY FOR
WINTHROP HARBOR TO NORTHERLY IS. IL.
SMALL CRAFT ADVISORY FROM NOON THURSDAY TO 6 AM CST FRIDAY FOR
NORTHERLY IS. TO CALUMET HARBOR IL.
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