571
FXUS63 KLOT 250812
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
212 AM CST THU DEC 25 2025
KEY MESSAGES
- CLOUDY CONDITIONS WILL CONTINUE TODAY WITH NEARLY STAGNANT
TEMPERATURES IN THE UPPER 30S (NORTH) AND LOW-MID 40S (SOUTH).
- ANOTHER PERIOD OF DRIZZLE AND RAIN SHOWERS IS LIKELY (60 TO
80% CHANCE) TONIGHT INTO FRIDAY. A PERIOD OF DENSE FOG MAY
OCCUR, AS WELL.
- A RETURN TO MORE WINTER-LIKE CONDITIONS IS ON TRACK TO ARRIVE
NEXT WEEK. WIND CHILLS FALLING TOWARD ZERO MAY RETURN TO THE
REGION AS EARLY AS MONDAY MORNING, FOLLOWED BY A RETURN OF
CHANCES FOR SNOW BY MIDWEEK.
DISCUSSION
ISSUED AT 212 AM CST THU DEC 25 2025
THROUGH FRIDAY:
A BROAD LOW-LEVEL BAROCLINIC/FRONTAL ZONE IS DRAPED ACROSS THE
MIDDLE MISSISSIPPI RIVER VALLEY AND LOWER GREAT LAKES REGION
THIS CHRISTMAS MORNING, BENEATH ANOMALOUSLY STRONG UPPER-LEVEL
RIDGING/QUASI-ZONAL FLOW POSITIONED ACROSS THE FAR NORTHERN
UNITED STATES. OUR AREA IS ENTRENCHED WITHIN THE BAROCLINIC
ZONE, LEADING TO OVERCAST SKIES, MIST/DRIZZLE, AREAS OF DENSE
FOG (LARGELY SOUTH OF I-80), AND OTHERWISE DAMP CONDITIONS.
TEMPERATURES RANGE FROM THE UPPER 30S NEAR THE WISCONSIN STATE
LINE TO NEARLY 50 DEGREES NEAR US-24.
THROUGHOUT THE MORNING, NORTHEASTERLY FLOW WILL CONTINUE TO
GRADUALLY INCREASE OVER THE REGION AS A 1030MB+ SURFACE HIGH
MOVES ACROSS SOUTHERN ONTARIO. WOULD EXPECT DRIZZLE AND FOG TO
HENCE GET PUSHED SOUTHWESTWARD WITH TIME, FOCUSING MORESO IN
CENTRAL ILLINOIS BY MID MORNING. WHILE A FEW BREAKS IN CLOUDS
MAY MATERIALIZE IN NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA THIS AFTERNOON, THE EXPECTATION IS FOR LARGELY CLOUDY
SKIES TO PREVAIL THROUGH DAYLIGHT HOURS MAKING FOR A "GRAY"
CHRISTMAS. LITTLE IN THE WAY OF TEMPERATURE ADVECTION WILL HOLD
TEMPERATURES TODAY CLOSE TO WHERE THEY ARE NOW, WITH THE UPPER
30S TO LOWER 40S NORTH OF I-88/EAST OF I-90, LOWER 40S BETWEEN
I-88 AND I-80, AND MID TO LOCALLY UPPER 40S SOUTH OF I-80.
THE NEXT RIPPLE PROPAGATING THROUGH THE QUASI-ZONAL FLOW ALOFT
WILL TRACK TOWARD THE REGION TONIGHT AND MOVE DIRECTLY OVERHEAD
TOMORROW MORNING. AREAS OF DRIZZLE WILL RETURN TONIGHT AHEAD OF
THE LOW, AND TRANSITION TO SHOWERS TOWARD DAYBREAK. A PERIOD OF
DENSE FOG MAY MATERIALIZE ALONG THE PATH OF THE CENTER OF THE
LOW AS WELL. AT THIS POINT, MOST GUIDANCE FAVORS THE SURFACE LOW
GETTING OUT OF HERE BY LATE MORNING, PROVIDING AN OPPORTUNITY
FOR TEMPERATURES TO SHOOT UP TOWARD THE UPPER 40S OR EVEN LOWER
50S BY EARLY AFTERNOON. IF THE SYSTEM ENDS UP MOVING SLOWER
THAN EXPECTED, TEMPERATURES WOULD VERIFY LOWER.
BORCHARDT
FRIDAY NIGHT THROUGH NEXT THURSDAY (NEW YEARS DAY):
A SURFACE HIGH AND ASSOCIATED MID-LEVEL RIDGING WILL BE
PIVOTING OVER NORTHERN IL AND NORTHWEST IN FRIDAY NIGHT AND
SHOULD BRING ANY LINGERING PRECIPITATION TO A CLOSE. WHILE IT
DOES LOOK LIKE A MUCH DRIER AIR MASS WILL MOVE IN WITH THE HIGH
ON SATURDAY, FORECAST SOUNDINGS CONTINUE TO SHOW SOME MODEST
LOW-LEVEL MOISTURE BEING TAPPED BENEATH THE SUBSIDENCE
INVERSION. THEREFORE, IT SEEMS LIKELY THAT AT LEAST SOME PARTLY
TO MOSTLY CLOUDY SKIES WILL BE SEEN ON SATURDAY. IN ADDITION TO
THE CLOUD COVER, THE WELL ADVERTISED BAROCLINIC ZONE WILL BE
SITTING OVER THE AREA AND SHOULD AID IN KEEPING TEMPERATURES
GENERALLY IN THE MID-40S ESPECIALLY FOR THOSE NORTH OF I-80 WITH
SLIGHTLY WARM READINGS (NEAR 50 IN SPOTS) FURTHER SOUTH.
HOWEVER, WITH WINDS EXPECTED TO BECOME MORE SOUTH-SOUTHEASTERLY
SATURDAY AFTERNOON, THERE REMAINS A CHANCE THAT HIGHS NEAR AND
SOUTH OF THE KANKAKEE RIVER COULD VERIFY IN THE LOWER 50S.
THE TAIL END OF THE WEEKEND AND EARLY PART OF NEXT WEEK
CONTINUES 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 THE NORTHERN
GREAT LAKES AND SOUTHERN ONTARIO. ATTACHED TO THIS LOW IS
EXPECTED TO BE A COLD FRONT THAT IS FORECAST TO BE DRAPED ACROSS
THE UPPER MIDWEST TO CENTRAL PLAINS SATURDAY AFTERNOON. THE
GENERAL GUIDANCE CONSENSUS IS THAT THIS COLD FRONT WILL BEGIN TO
MOVE TOWARDS NORTHERN IL AND NORTHWEST IN SATURDAY NIGHT WITH A
PASSAGE LOOKING TO OCCUR SOMETIME ON SUNDAY. FURTHERMORE, THE
SIGNAL REMAINS FOR A SECONDARY SURFACE LOW TO DEVELOP IN THE
CENTRAL PLAINS AND LIFT NORTHWARD TOWARDS THE SOUTHERN GREAT
LAKES AND OHIO RIVER VALLEY SATURDAY NIGHT. WHILE THE EVOLUTION
IS GENERALLY UNCHANGED IN LATEST GUIDANCE SUITES, THE TRACK OF
THE LOW HAS SHIFTED A BIT FARTHER NORTH. SINCE MOST GUIDANCE
(70-80% OF ENSEMBLE MEMBERS) HAS THE SECONDARY LOW NOW MOVING
OVER NORTHERN IL AND NORTHWEST IN, IT SEEMS THAT OUR AREA WILL
BE IN A BETTER POSITION TO GET TRUE RAIN AS OPPOSED TO DRIZZLE
AS THOUGHT ORIGINALLY. IN FACT, THE LATEST ENSEMBLE
PROBABILITIES FOR AT LEAST 0.5 INCHES OF RAIN IN OUR AREA HAS
INCREASED TO 30-40% PARTICULARLY FOR THOSE SOUTHEAST OF I-55.
THESE RAINFALL AMOUNTS DON'T IMMEDIATELY LOOK CONCERNING AT
FACE VALUE, BUT WHEN YOU SEE FROST DEPTHS AROUND 4 INCHES ACROSS
THE AREA, THE POTENTIAL IS THERE FOR SOME HYDRO ISSUES. WITH
THIS SHIFT BEING A SOMEWHAT RECENT TREND, THE CONFIDENCE ON
THESE RAIN AMOUNTS ACTUALLY OCCURRING IN OUR FORECAST AREA
REMAINS LOW BUT WILL BE MONITORED CLOSELY GOING FORWARD. ASIDE
FROM THE RAIN, TEMPERATURES ON SUNDAY COULD ALSO BE NOTABLY
WARMER THAN ORIGINALLY THOUGHT WITH MOST OF THE AREA IN THE 50S
AND THOSE NEAR AND SOUTH OF THE KANKAKEE RIVER NEARING 60S.
HOWEVER, WITH SOME NEW UNCERTAINTIES IN THE ACTUAL TIMING OF THE
FRONT PASSAGE AND WHERE THE SECONDARY LOW WILL TRACK, THE
TEMPERATURE FORECAST FOR SUNDAY IS VERY LOW CONFIDENCE. SO FOR
THAT REASON THE OFFERED TEMPERATURES FOR THE NBM WHERE GENERALLY
MAINTAINED, BUT DID COOL TEMPERATURES IN OUR NORTHERN COUNTIES
(NEAR THE IL-WI LINE) TO TEASE THE POTENTIAL FOR AN EARLIER
FRONT ARRIVAL.
IN THE WAKE OF THE FRONT ON SUNDAY, TEMPERATURES WILL BE
QUICKLY COOLING INTO THE TEENS TO LOWER 20S BY MONDAY MORNING.
WITH THIS ADVANCING COLD AIR THERE IS ALSO EXPECTED TO BE SOME
TRANSITION OF RAIN OVER TO SNOW DURING THE EVENING HOURS ON
SUNDAY. NOW DEPENDING ON HOW QUICKLY TEMPERATURES COOL AND HOW
FAST THE DRIER AIR ARRIVES WILL ULTIMATELY DETERMINE IF THE SNOW
ACTUALLY ACCUMULATES OR IF WE JUST GET SOME FLURRIES. AT THIS
POINT IT SEEMS THE GENERAL CONSENSUS IS FOR MOSTLY FLURRIES WITH
PERHAPS A COUPLE TENTHS OF ACCUMULATION BUT WILL AGAIN NEED TO
KEEP AN EYE ON TRENDS WITH THIS PERIOD TO KNOW FOR CERTAIN.
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 IN EXCESS OF
30-35 MPH (POSSIBLY AS UP TO 40-45 MPH) LATE SUNDAY INTO THE
DAY ON MONDAY. WITH TEMPERATURES SUNDAY NIGHT FORECASTED TO NOW
BE A BIT WARMER (IN THE TEENS TO LOWER 20S), IT APPEARS WIND
CHILLS MAY BE MORE IN THE SINGLE DIGIT RANGE AS OPPOSED TO SUB-
ZERO. REGARDLESS, THE BLUSTERY WINDS WILL STILL MAKE IT
UNPLEASANT OUTDOORS SUNDAY NIGHT AND AGAIN ON MONDAY.
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
MEMBERSHIP CONTINUES 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, THE SIGNAL REMAINS FOR A WINTRY
SYSTEM TO BE IN THE GREAT LAKES REGION TOWARDS NEW YEARS DAY BUT
WHETHER OR NOT WE ACTUALLY SEE ANY PRECIPITATION FROM IT IS
STILL NOT CLEAR SO STAY TUNED.
YACK
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1059 PM CST WED DEC 24 2025
KEY AVIATION MESSAGES:
- PERIOD OF LOW-MVFR OVERNIGHT, WITH A PERIOD OF IFR POSSIBLE
ESPECIALLY AT KRFD/KDPA/KGYY THROUGH 09-10Z.
- PREVAILING MVFR CIGS EXPECTED MUCH OF THE DAY THURSDAY,
THOUGH COULD BE BRIEF IMPROVEMENT TO VFR.
- MVFR DEVELOPS MORE SOLIDLY FRIDAY EVENING, LIKELY LOWERING TO
IFR AFTER MIDNIGHT WIT DRIZZLE/SHOWERS/FOG REDEVELOPING.
- NORTHEAST WINDS 10-15 KT BECOME EAST-SOUTHEAST THURSDAY
EVENING.
A WEAK SURFACE LOW PRESSURE WAVE WAS EVIDENT OVER WESTERN IL
LATE THIS EVENING, AND WILL CONTINUE TO TRACK QUICKLY EAST
ALONG A NEARLY STATIONARY WARM FRONT ACROSS CENTRAL IL/IN
OVERNIGHT. MOIST ASCENT AHEAD OF THIS WAVE HAS ALLOWED FOR
DRIZZLE AND LIGHT RAIN TO DEVELOP EARLIER THIS EVENING, LOWERING
CIGS TO LOW-MVFR ACROSS THE TERMINALS AND TO IFR/LIFR WEST AND
SOUTH OF THE TERMINALS. PERSISTENT LIGHT DRIZZLE WILL PERSIST
UNTIL THE SURFACE LOW MOVES EAST OF THE AREA AROUND 09-10Z, AND
MAY ALLOW FOR CONTINUED DETERIORATION TO IFR BRIEFLY AT THE
TERMINALS ESPECIALLY RFD/DPA/GYY. WINDS WILL THEN SHIFT
NORTHEASTERLY BEHIND THE DEPARTING SURFACE WAVE, WHICH WILL DRAW
DRIER LOW-LEVEL AIR INTO THE AREA BY MORNING AND SHOULD ALLOW
IMPROVEMENT BACK TO MID-HIGH RANGE MVFR (AND POTENTIALLY EVEN
VFR FOR A TIME). HAVE INDICATED PREVAILING MVFR CIGS THROUGH
MUCH OF THE DAY THURSDAY, THOUGH WITH SOMEWHAT LOWER CONFIDENCE
GIVEN SOME VFR POTENTIAL.
ANOTHER AREA OF LOW PRESSURE IS FORECAST TO APPROACH THE AREA
THURSDAY NIGHT, WITH WINDS SHIFTING EAST/SOUTHEAST 10-15 KT BY
EVENING AND PULLING LOW-LEVEL MOISTURE BACK INTO THE AREA. IN
ADDITION, DRIZZLE/SHOWERS AND FOG WILL LIKELY DEVELOP LATER IN
THE EVENING AND OVERNIGHT WITH IFR CONDITIONS BECOMING LIKELY BY
FRIDAY MORNING.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...DENSE FOG ADVISORY UNTIL 6 AM CST EARLY THIS MORNING FOR
ILZ008-ILZ010-ILZ019-ILZ023-ILZ032-ILZ033-ILZ039.
IN...DENSE FOG ADVISORY UNTIL 6 AM CST /7 AM EST/ EARLY THIS
MORNING FOR INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO NOON CST FRIDAY
FOR WINTHROP HARBOR TO NORTHERLY IS. IL.
SMALL CRAFT ADVISORY FROM NOON TODAY TO 6 AM CST FRIDAY FOR
NORTHERLY IS. TO CALUMET HARBOR IL.
VISIT US AT WEATHER.GOV/CHICAGO
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