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FXUS63 KLOT 270306
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
906 PM CST FRI DEC 26 2025
KEY MESSAGES
- LOCALLY DENSE FOG MAY REDEVELOP ACROSS PORTIONS OF THE AREA
LATE TONIGHT INTO SATURDAY MORNING.
- LIGHT SHOWERS AND DRIZZLE ALONG WITH AREAS OF FOG WILL LIKELY
DEVELOP SATURDAY NIGHT, WITH SHOWERS CONTINUING SUNDAY.
- THERE IS A CHANCE OF THUNDERSTORMS, POSSIBLY SEVERE, SOUTH OF
I-80 SUNDAY AFTERNOON/EVENING.
- VERY WINDY AND MUCH COLDER SUNDAY NIGHT-MONDAY. SNOW SHOWERS
MAY CAUSE SOME ACCUMULATION AND ASSOCIATED TRAVEL IMPACTS.
UPDATE
ISSUED AT 906 PM CST FRI DEC 26 2025
AS NOTED IN THE DISCUSSION BELOW, THE SETUP TONIGHT INTO
SATURDAY IS FAVORABLE FOR THE GRADUAL BUILDING DOWN OF STRATUS
AND EVENTUAL FOG DEVELOPMENT. THE OVERALL THINKING HASN'T
CHANGED MUCH THIS EVENING, THOUGH FOR MESSAGING PURPOSES DID HIT
THE POTENTIAL FOR DENSE FOG A BIT HARDER IN THE GRIDDED
FORECAST. GIVEN THAT THIS WILL NOT BE A RADIATIONAL COOLING
DRIVEN FOG EPISODE, IT WILL TAKE SOME TIME FOR DENSE FOG TO
MATERIALIZE WITHIN THE CWA, THOUGH VISIBILITIES ARE ALREADY
BEGINNING TO CREEP DOWN OUT CLOSER TO THE MS RIVER.
PLANNING TO PUT OUT A GRAPHICAL NOWCAST TO HIGHLIGHT THE
POTENTIAL FOR AREAS OF DENSE FOG (AND POSSIBLE NEED FOR A DENSE
FOG ADVISORY) IN THE PRE-DAWN HOURS THROUGH THE MID TO LATE
MORNING. THE MAIN AREAS OF CONCERN ARE ROUGHLY NEAR AND WEST OF
A FOWLER, IN TO ANTIOCH, IL LINE. IT'S IN THE REALM OF
POSSIBILITY FOR PATCHY DENSE FOG TO LINGER TOWARD OR PAST NOON
ACROSS PORTIONS OF INTERIOR NORTHERN ILLINOIS. AS ALREADY
DEPICTED IN THE GRIDS, IT APPEARS UNLIKELY THAT THE STRATUS WILL
BE ABLE TO ERODE SATURDAY AFTERNOON.
LOOKING AHEAD TO SATURDAY NIGHT INTO EARLY SUNDAY, FOG
DEVELOPMENT APPEARS LIKELY ONCE AGAIN, ALONG WITH GRADUALLY
INCREASING COVERAGE OF LIGHT SHOWERS AND DRIZZLE.
CASTRO
DISCUSSION
ISSUED AT 1248 PM CST FRI DEC 26 2025
THROUGH SATURDAY:
WHILE THE DENSE FOG FROM EARLY THIS MORNING HAS DISSIPATED, A
LOW-LEVEL STRATUS DECK REMAINS PERSISTENT ACROSS THE AREA, THUS
MAKING FOR ANOTHER GLOOMY AFTERNOON. WITH NO SIGNS OF SCATTERING
THIS DECK OUT ANYTIME SOON, TEMPERATURES THROUGH SATURDAY ARE
EXPECTED TO LARGELY REMAIN STEADY THROUGH THE DAYTIME AND
NIGHTTIME HOURS. ACCORDINGLY, ONLY ABOUT A 5 TO 10 DEGREE
DIFFERENCE BETWEEN THE DAILY HIGH AND LOW TEMPERATURE IS
ANTICIPATED, WITH LOWS GENERALLY IN THE 30S AND HIGHS ON
SATURDAY IN THE 40S.
THE MAIN FORECAST CONCERN WE CONTINUE TO MONITOR IS THE THREAT
FOR ANOTHER PERIOD OF DENSE FOG ACROSS PORTIONS OF THE AREA LATE
TONIGHT INTO SATURDAY MORNING. RADIATIONAL COOLING LOOKS TO BE
SIGNIFICANTLY LIMITED (IF NOT NON-EXISTANT) TONIGHT, OWING TO
THE PERSISTENT STATUS DECK. WHILE THIS IS NOT TYPICALLY A GOOD
RECIPE FOR DENSE FOG DEVELOPMENT, LIGHT AND VARIABLE WINDS ARE
EXPECTED TONIGHT AS A SURFACE HIGH PRESSURE RIDGE MOVES
OVERHEAD. THIS IN COMBINATION WITH CONTINUED AMPLE LOW-LEVEL
MOISTURE IN PLACE (DEW POINT DEPRESSIONS OF ONLY A COUPLE OF
DEGREES), CONDITIONS WILL BE FAVORABLE TO SUPPORT THE BUILD DOWN
OF THIS STATUS DECK TO SURFACE TONIGHT. CURRENT THINKING IS
THAT THE HIGHEST POTENTIAL FOR DENSE FOG TONIGHT INTO SATURDAY
MORNING WILL LARGELY BE ACROSS INTERIOR SECTIONS OF IL (MAINLY
WEST OF CHICAGO). WE THUS COULD BE LOOKING AT THE NEED FOR
ANOTHER POTENTIAL DENSE FOG ADVISORY FOR SOME AREAS AS WE GET A
BETTER HANDLE ON OBSERVATION TRENDS LATER THIS EVENING.
SIMILAR TO TODAY, VISIBILITIES ARE LIKELY TO STEADILY IMPROVE
INTO THE EARLY AFTERNOON AS THE FOG DISSIPATES. HOWEVER, WITH
THE PROSPECTS OF CONTINUED STRATUS, ANOTHER CLOUDY DAY IS
ANTICIPATED, WITH HIGHS GENERALLY IN THE 40S.
KJB
SATURDAY NIGHT THROUGH FRIDAY:
SATURDAY EVENING, WE'LL FIND A WARM FRONT LIFTING NORTHWARD
ACROSS CENTRAL IL AHEAD OF AN IMPENDING SURFACE LOW WORKING
ACROSS THE CENTRAL PLAINS. THIS SYSTEM WILL PROVIDE OUR NEXT
OPPORTUNITY FOR RAIN, SNOW, AND MAYBE EVEN A FEW THUNDERSTORMS.
ISOLATED TO SCATTERED SHOWERS MAY BLOSSOM OUT AHEAD OF THE WARM
FRONT DURING THE EVENING. THE BOUNDARY LOOKS TO LIFT INTO OUR
CWA TOWARD THE END OF THE EVENING. ACCORDINGLY, WE'LL SEE
TEMPERATURES RISING DURING THE NIGHT, MAYBE BY AS MUCH AS 4 OR 5
DEGREES BEFORE SUNRISE SUNDAY.
THIS STORM WILL INTENSIFY RAPIDLY AFTER THE PARENT UPPER TROUGH
QUICKLY DIGS SOUTH FROM SOUTHERN CANADA INTO THE NORTHERN
PLAINS SATURDAY NIGHT. IN FACT, THE LATEST GFS AND EURO HAVE
THIS THING NEARLY BOMBING DROPPING THE CENTRAL PRESSURE 22-23 MB
BETWEEN EARLY SUNDAY AND EARLY MONDAY. THE PEAK OF THESE
PRESSURE FALLS WILL OCCUR JUST AS THE STORM MOVES ACROSS THE
REGION. PRECIP COVERAGE WILL EXPAND AROUND THE WARM FRONT SUNDAY
MORNING AS THE STORM STARTS TO QUICKLY DEEPEN. WIDESPREAD
MODERATE TO HEAVY RAINFALL IS EXPECTED ALONG THE STORM'S WARM
CONVEYOR AS IT REELS TONS OF LAYER MOISTURE INTO THE REGION.
THIS WILL IMPACT THE LOCAL AREA DURING THE AFTERNOON AND EARLY
EVENING WHEN SURFACE DEWPOINTS WILL EXCEED 60F IN AT LEAST OUR
SOUTHERN CWA, BUT POSSIBLY A MAJORITY OF THE AREA. PREVIOUSLY,
GUIDANCE HAD BEEN IN PRETTY SOLID AGREEMENT ON THE STORM
TRACKING IMMEDIATELY ACROSS THE CWA FROM SW TO NE. THIS OUTCOME
WOULD FAVOR AREAS ROUGHLY SOUTH AND EAST OF I-55 TO RECEIVE THE
MOST RAIN. WHILE THAT STILL GENERALLY LOOKS TRUE, A NUMBER OF
RECENT CAMPS HAVE TRENDED SLIGHTLY NORTH AND WEST WITH THE STORM
TRACK. THE LATEST EXTENDED RAP, WHICH LOOKS THROUGH 18Z SUNDAY,
IS ON BOARD WITH THE FARTHER NW TRACK AND PULLS 60S DEWPOINTS
UP TO THE I-88 CORRIDOR AND WEST OF THE FOX VALLEY. IF THIS NW
SOLUTION VERIFIES, IT WOULD PULL THE BETTER SOAKING RAIN AND
THUNDERSTORM ENVIRONMENTS SLIGHTLY NORTH AND WEST DEEPER INTO
THE CWA (MORE ON STORM POTENTIAL BELOW). ACCORDINGLY, HIGHER POP
VALUES AND EXCEEDANCE PROBS FROM THE BLEND ARE ALSO TRENDING
SLIGHTLY NORTH AND WEST. EVERY PIECE OF LATEST DETERMINISTIC
GUIDANCE RESOLVES OVER AN INCH OF QPF SOMEWHERE AROUND THE CWA,
MOST OF THAT FOUND NEAR AND EAST OF I-55. GENERALLY LESS THAN AN
INCH IS FAVORED ON A BROAD SCALE, THOUGH.
REGARDING THE THUNDER POTENTIAL, MODEST BL DESTABILIZATION WILL
TAKE PLACE IN THE AFTERNOON AND EVENING, PRIMARILY SOUTH OF
I-80, AMID THOSE 60S TDS WITH AS MANY AS A FEW TO SEVERAL
HUNDRED JOULES OF CAPE BEING MODELED. THE LACK OF BUOYANCY,
ESPECIALLY ABOVE THE LOWEST COUPLE OF HUNDRED MILLIBARS, SHOULD
KEEP ANY CONVECTION ON THE SHALLOWER SIDE. BUT WE'LL FIND
SIGNIFICANT DYNAMIC FORCING AHEAD OF THE STORM AND ITS COLD
FRONT THANKS TO THOSE RAPID PRESSURE/HEIGHT FALLS. PLUS, A
STRONG JET WILL DEVELOP ATOP THE TIGHTENING BAROCLINIC ZONE
OFFERING 30+ KT OF 0-1 KM SHEAR AND AROUND 50 KT OF EFFECTIVE
SHEAR. THIS COULD LEAD TO AN ORGANIZED LINE OF SHALLOW
CONVECTION, ONE THAT MAY NOT EVEN PRODUCE MUCH LIGHTNING BUT
COULD POSSIBLY BRING SOME STRONG WIND GUSTS TO THE SURFACE.
LOCALLY DAMAGING GUSTS EVEN APPEAR WITHIN REACH, WHICH
CORRESPONDS WELL WITH SPC'S DAY 3 MARGINAL OUTLOOK IN OUR SOUTH.
THE THUNDERSTORM POTENTIAL LARGELY FAVORS SOUTHERN AND
SOUTHEASTERN PORTIONS OF OUR CWA WHERE THE BETTER SHEAR AND
MOISTURE FEED WILL BE FOUND. WITH THIS RECENT TREND IN THE STORM
TRACK TOWARD THE NW, CONVECTION NOW APPEARS MORE ATTAINABLE
INTO THE SOUTHERN CHICAGO METRO AREA, IF NOT EVEN FARTHER NW.
ACCORDINGLY, PIGGYBACKED OFF THE OVERNIGHT SHIFT TO EXPAND
SLIGHT THUNDER CHANCES FROM THE BLEND'S SOLUTION TO INCLUDE
AREAS ROUGHLY SOUTH OF I-80 AND EAST OF I-55.
IN THE COLD ADVECTION WING, PRECIP IS EXPECTED TO TRANSITION TO
A WINTRY MIX SUNDAY EVENING AND EVENTUALLY TO ALL SNOW LATER IN
THE NIGHT. THE SIGNAL FOR TRUE SNOW SHOWERS VS FLURRIES IS
GROWING WITH TIME, MAINLY IN OUR NORTH, AS IS THE POTENTIAL FOR
ACCUMULATIONS. SNOW IS EXPECTED TO CONTINUE INTO MONDAY MORNING
AND TAPER OFF TOWARD MIDDAY. IT'S POSSIBLE THAT PARTS OF THE
AREA WILL SEE A COATING OF SNOW ON ROADS IN TIME FOR THE MONDAY
MORNING COMMUTE.
WINDY CONDITIONS ARE ALSO ANTICIPATED AROUND THE SYSTEM SUNDAY
EVENING THROUGH MONDAY. WESTERLY GUSTS BETWEEN 25 AND 30 MPH
LATER SUNDAY EVENING WILL BUILD TO CLOSER TO 40 MPH BY MONDAY
MORNING. WINDS SHOULD GRADUALLY EASE DURING THE LATE AFTERNOON
AND EVENING.
THESE WINDS WILL MAKE THE COOLER DAY ON MONDAY FEEL EVEN
COLDER. STRONG POST-FRONTAL COLD ADVECTION WILL PULL MORNING
LOWS DOWN INTO THE TEENS AND LOWER 20S ON MONDAY WITH ONLY LOWER
AND MIDDLE 20S FORECAST IN THE AFTERNOON. WIND CHILLS ARE
FORECAST IN THE SINGLE DIGITS ABOVE AND BELOW ZERO IN THE
MORNING, AND SHOULD FAIL TO EXCEED SINGLE DIGITS ABOVE ZERO
THROUGHOUT THE DAY. UPPER 20S AND LOWER 30S ARE ANTICIPATED INTO
MIDWEEK BEFORE ANOTHER SHOT OF COLD AIR LOOKS TO ARRIVE JUST IN
TIME FOR THE NEW YEAR.
DOOM
AVIATION /00Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 548 PM CST FRI DEC 26 2025
AVIATION FORECAST CONCERNS:
- GRADUAL DETERIORATION TO IFR CONDITIONS LIKELY OVERNIGHT.
- AREAS WEST OF THE CHICAGO METRO CORE MORE LIKELY TO SEE
LIFR/VLIFR CONDITIONS BY SATURDAY MORNING.
- LOW CONFIDENCE IN IMPROVEMENT BEYOND HIGH-END IFR SATURDAY.
SURFACE HIGH PRESSURE WAS DEVELOPING EASTWARD ACROSS THE
MISSISSIPPI VALLEY EARLY THIS EVENING, AND WILL BE ACROSS THE
TERMINALS OVERNIGHT. LIGHT VARIABLE WINDS, SUBSIDENCE WITHIN THE
RIDGE AXIS AND LACK OF THICKER CLOUD COVER ABOVE EXISTENT
EXTENSIVE LOW STRATUS DECK IS EXPECTED TO RESULT IN A GRADUAL
BUILD DOWN OF CURRENT LOW- MVFR STRATUS INTO IFR THROUGH LATE
THIS EVENING. LIFR/DEVELOPING VLIFR CONDITIONS IN STRATUS/FOG
ACROSS CENTRAL IA ARE EXPECTED TO SPREAD INTO INTERIOR NORTHERN
IL BY MORNING, WITH GUIDANCE GENERALLY HIGHLIGHTING AREAS WEST
OF THE CORE CHICAGO METRO TERMINALS (DPA- WEST AND ESPECIALLY
RFD) FOR THE GREATEST LIFR/VLIFR POTENTIAL IN OUR FORECAST AREA.
HAVE INDICATED A TEMPO FOR 1/2SM AND OVC002 FOR RFD TOWARD
DAYBREAK, WHILE CONFIDENCE FOR LOWER CONDITIONS DECREASES WITH
EASTWARD EXTENT INTO THE CHICAGO AREA.
THE SURFACE HIGH PRESSURE CENTER WILL PULL AWAY FROM THE AREA
TO THE EAST SATURDAY MORNING, WITH LIGHT/VARIABLE WINDS TURNING
SOUTHEAST AND INCREASING TO AROUND 10 KTS. THIS SHOULD HELP
VISIBILITIES TO IMPROVE AND THE STRATUS TO LIFT SOMEWHAT, THOUGH
THERE IS QUITE A SPREAD IN AVAILABLE MODEL GUIDANCE WITH
RESPECT TO THE DEGREE OF IMPROVEMENT IN CIG HEIGHTS INTO THE
AFTERNOON. MUCH OF THE DETERMINISTIC HIGH-RES GUIDANCE WOULD
SUGGEST IFR CIGS WILL LINGER THROUGH THE DAY, RATHER THAN
IMPROVE TO MVFR OR SCATTER TO VFR AS DEPICTED BY SOME MODELS.
THINKING AT THIS TIME IS THAT IMPROVEMENT TO SOLID MVFR IS IS
SOMEWHAT UNLIKELY, THOUGH CONFIDENCE THESE TRENDS BEYOND MIDDAY
IS LOW. INCREASING LOW LEVEL SOUTH FLOW LATE IN THE DAY/EVENING
DOES LOOK TO LEAD TO FURTHER MOISTENING AHEAD OF ANOTHER
DISTURBANCE SATURDAY NIGHT, WHICH WOULD PERHAPS SUPPORT A
DOWNWARD TREND IN CEILING HEIGHTS BY/DURING THE EVENING HOURS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING FOR
WINTHROP HARBOR IL TO GARY IN.
GALE WATCH FROM SUNDAY EVENING THROUGH LATE MONDAY NIGHT FOR
GARY TO BURNS HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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