373
FXUS63 KLOT 242051
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
251 PM CST WED DEC 24 2025
KEY MESSAGES
- A PERIOD OF DRIZZLE AND FOG IS EXPECTED TONIGHT. THE GREATEST
POTENTIAL FOR DENSE FOG TONIGHT IS IN LOCATIONS SOUTH OF
I-80.
- CLOUDY CONDITIONS WILL CONTINUE ON CHRISTMAS DAY 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) 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 251 PM CST WED DEC 24 2025
THROUGH THURSDAY/CHRISTMAS DAY:
THE MAIN FORECAST CONCERN IN THE NEAR TERM (THROUGH CHRISTMAS
DAY) REMAINS ON THE LIKELIHOOD OF DRIZZLE AND FOG TONIGHT.
THUS FAR, DRIZZLE HAS STRUGGLED TO GET GOING UPSTREAM OF OUR
AREA EARLY THIS AFTERNOON. HOWEVER, THE EXPECTATION IS STILL
THAT DRIZZLE WILL BLOSSOM RELATIVELY QUICKLY LATE THIS AFTERNOON
AND EVENING AS THE LIFT PROVIDED BY A SHORTWAVE IMPULSE CRESTING
THE TOP OF AN UPPER-LEVEL RIDGE CENTERED JUST TO OUR WEST
INCREASINGLY OVERLAPS THE INBOUND PUSH OF LOW-LEVEL ISENTROPIC
ASCENT/WARM AIR ADVECTION FROM THE SOUTHWEST. THE QPF OUTPUT
FROM BOTH HI-RES AND GLOBAL MODEL GUIDANCE REMAINS QUITE ROBUST
CONSIDERING THE SUBTLETIES OF THIS SETUP, SUGGESTING THAT THE
DRIZZLE SHOULD BE FAIRLY WIDESPREAD AND POSSIBLY INTERSPERSED
WITH SOME MORE TRUE "SHOWERY" ELEMENTS. THUS, FELT COMFORTABLE
LARGELY MAINTAINING THE INHERITED POPS WITH THE EXPECTATION THAT
MOST LOCATIONS SHOULD PICK UP SOMEWHERE BETWEEN A HUNDREDTH AND
A TENTH OF AN INCH OF PRECIPITATION.
INCREASING DEW POINTS THIS EVENING FROM BOTH THE DRIZZLE AND
THE NORTHWARD ADVECTION OF A MORE MOISTURE-LADEN LOW-LEVEL AIR
MASS, COMBINED WITH SLACKENING WINDS WILL ALSO LIKELY RESULT IN
THE DEVELOPMENT OF FOG IN SOME LOCATIONS TONIGHT. HI-RES
GUIDANCE PARTICULARLY CONTINUES TO EXHIBIT A STRONG SIGNAL FOR
DENSE FOG IN AREAS SOUTH OF I-80. GAVE STRONG CONSIDERATION TO
THE ISSUANCE OF A DENSE FOG ADVISORY, PARTICULARLY IN OUR
SOUTHERNMOST COUNTIES SOUTH OF THE KANKAKEE RIVER WHERE THIS
DENSE FOG SIGNAL IS ALMOST UBIQUITOUS ACROSS THE HI-RES GUIDANCE
SUITE. AFTER COORDINATING WITH SURROUNDING WFOS, ELECTED TO
HOLD OFF ON ISSUING AN ADVISORY FOR NOW WITH THERE STILL BEING
SOME UNCERTAINTY ON THE NORTHWARD EXTENT OF THE DENSE FOG BANK.
WILL NONETHELESS PASS ALONG THESE CONCERNS TO THE INCOMING
EVENING SHIFT, WHO WILL HAVE THE LUXURY OF SEEING HOW
OBSERVATIONAL TRENDS ARE PANNING OUT AFTER SUNSET AND SHOULD BE
IN A BETTER POSITION TO GAUGE JUST HOW FAR NORTH ANY DENSE FOG
SHOULD GET TONIGHT WITH HIGHER CONFIDENCE.
THE THREAT FOR BOTH DRIZZLE AND FOG SHOULD END FROM NORTH TO
SOUTH OVERNIGHT INTO CHRISTMAS MORNING AS A WEAK COLD FRONT
DRIFTS SOUTHWARD THROUGH THE AREA AND DRIER LOW-LEVEL AIR BEING
FUNNELED SOUTHWARD BY A HIGH PRESSURE SYSTEM TRACKING EASTWARD
FROM MANITOBA INTO ONTARIO FILTERS IN BEHIND IT. THE LOW-LEVEL
DRY AIR ADVECTION COUPLED WITH LARGE-SCALE SUBSIDENCE DRIVING
INVERSION HEIGHTS LOWER SHOULD HAVE A NET EFFECT OF THINNING THE
EXPANSIVE OVERHEAD STRATUS DECK ON CHRISTMAS DAY. WOULDN'T BE
SURPRISED TO SEE SOME LOCATIONS LOSE THE STRATUS ALTOGETHER BY
THE AFTERNOON, BUT EVEN IF THAT OCCURS, WHAT LOOKS TO BE A
FAIRLY THICK UPPER-LEVEL CLOUD CANOPY SHOULD STILL NEVERTHELESS
BLUNT SOLAR INSOLATION TO AN APPRECIABLE DEGREE. THUS, BETWEEN
THE CLOUD COVER AND THE LARGELY NORTHEASTERLY/ONSHORE FLOW
TRAJECTORIES, AIR TEMPERATURES WILL NOT CHANGE MUCH OVER THE
COURSE OF THE DAYTIME TOMORROW -- PERHAPS RISING A MODEST 3-6
DEGREES IN SOME LOCATIONS AND ESSENTIALLY FLATLINING IN OTHER
SPOTS.
OGOREK
THURSDAY/CHRISTMAS NIGHT THROUGH WEDNESDAY:
EARLY THURSDAY, A MID LEVEL SHORTWAVE IMPULSE WILL EJECT EAST
OFF THE NEW MEXICO ROCKIES AND QUICKLY PROPAGATE ACROSS THE
CENTRAL CONUS. AT THE SURFACE, THIS WILL EQUATE TO A DEEPENING
CENTER OF LOW PRESSURE WHICH WILL WORK INTO THE LOWER MIDWEST
THURSDAY EVENING AND CUT ACROSS NORTH-CENTRAL IL THURSDAY NIGHT
INTO EARLY FRIDAY. THE SYSTEM'S WARM FRONT WILL BE DRAPED ACROSS
CENTRAL IL DURING THE DAY ON THURSDAY WITH SOME INSTANCES OF
DRIZZLE POSSIBLE SOUTH OF THE LOCAL AREA. PRECIP COVERAGE IS
EXPECTED TO EXPAND OUT AHEAD OF THE LOW DURING THE LATTER HALF
OF THURSDAY AS IT DEEPENS AND EVENTUALLY PHASES WITH THE HIGHER
AMPLITUDE LOW LEVEL TROUGH ACROSS THE UPPER MIDWEST. WE COULD
SEE LIGHT RAIN OR DRIZZLE OUT AHEAD OF THIS STORM REACH OUR CWA
AS EARLY AS THURSDAY EVENING, PARTICULARLY WEST OF CHICAGOLAND.
DENSER COVERAGE WILL WORK OVER THE AREA DURING THE NIGHT AS THE
WARM FRONT SURGES NORTHWARD IMMEDIATELY AHEAD OF THE PASSING
SYSTEM. MODEL QPF OUTPUT FAVORS AREAS ALONG AND JUST NORTHEAST
OF THE LOW TRACK TO RECEIVE THE MOST PRECIP AND, WHILE THERE
REMAINS UNCERTAINTY IN THE STORM TRACK, THIS MAY EQUATE TO THE
NORTHERN HALF OR SO OF THE CWA. THE MORE FOCUSED FORCING AND
SLIGHTLY COOLER MID LEVEL AIR IN THIS CORRIDOR COULD OFFER A
PERIOD OR TWO OF MODERATE RAIN RATES, BUT ENSEMBLE QPF OUTPUT
GENERALLY MAXES OUT AROUND A COUPLE TENTHS OF AN INCH.
PRECIP WILL DEPART TO THE EAST BY THE END OF FRIDAY MORNING.
RELATIVE HIGH PRESSURE WILL SETTLE INTO THE REGION BEHIND THE
DEPARTING SYSTEM AND AHEAD OF ANOTHER IMPENDING WAVE. THIS
SHOULD KEEP THE WEATHER RATHER QUIET FOR THE BETTER OF FRIDAY
AND ALL OF SATURDAY. HOWEVER, A LINGERING BAROCLINIC ZONE
MEANDERING ABOUT THE REGION MAY KEEP THE LOW LEVELS SATURATED
AND THE MOSTLY CLOUDY SKIES AROUND THROUGH THE WEEKEND.
QUITE A BIT OF UNCERTAINTY REVOLVES AROUND SOME ABNORMAL
TEMPERATURE TRENDS THIS WEEKEND. MUCH OF THE AREA IS EXPECTED TO
SEE TEMPERATURES WARM OVERNIGHT THURSDAY NIGHT AS THE WARM
FRONT LIFTS INTO OUR AREA AHEAD OF THE IMPENDING LOW. DURING THE
DAY ON FRIDAY, THE COLD ADVECTION IN THE WAKE OF THE LOW IS NOT
ANTICIPATED TO OFFSET DIURNAL HEATING ALL TOO MUCH, BUT THERE
IS UNCERTAINTY IN HOW MUCH TEMPS WILL BE ABLE TO CLIMB ON
FRIDAY. A GOOD CONSENSUS AMONG GUIDANCE IS A RANGE OF HIGHS FROM
THE MID 50S TOWARD CENTRAL IL TO THE MID 40S NEAR THE WI STATE
LINE, BUT A LOT OF THIS RIDES ON WHERE WE'LL FIND TEMPERATURES
TO START THE DAY ON FRIDAY WHILE THE LOW PASSES THROUGH. SIMILAR
HIGHS ARE EXPECTED ON SATURDAY. SATURDAY EVENING, THAT SECOND
WAVE WILL BE APPROACHING FROM THE SOUTHWEST AND ITS WARM FRONT
LOOKS TO LIFT INTO AT LEAST SOUTHERN PORTIONS OF THE CWA. THIS
MAY HINDER DIURNAL COOLING FOR A GOOD PORTION OF THE AREA.
STRONG COLD ADVECTION LOOKS TO TAKE PLACE BEHIND THE SYSTEM
BEGINNING EARLY SUNDAY, AND A NUMBER OF MEDIUM-RANGE CAMPS FAVOR
TEMPERATURES COOLING ALL DURING THE DAY. THERE'S SOME NOTABLE
DISAGREEMENT ON EXACT NUMBERS, BUT MOST OF SUNDAY AFTERNOON
COULD BE SPENT IN THE 30S, ESPECIALLY NORTHWEST OF I-55.
INCREASING WINDS BEHIND THE SYSTEM MAY PROVIDE WIND CHILLS IN
THE UPPER TEENS AND 20S BEFORE THE DUSK, AND ONLY COOLING FROM
THERE.
REGARDING PRECIP CHANCES WITH THIS SECOND SYSTEM, SCATTERED
SHOWERS MAY ACCOMPANY THE LOW CENTER AS IT WORKS ACROSS NORTH-
CENTRAL IL SUNDAY MORNING. BETTER CHANCES WILL ACTUALLY BLOSSOM
BEHIND THE DEPARTING LOW SUNDAY AFTERNOON ALONG THE HEAVILY
SLOPED FACE OF THE STORM'S COLD FRONT. SHOWER COVERAGE AND RATES
DURING THE AFTERNOON LOOK HIGHEST SOUTH AND EAST OF I-55, BUT
PRECIP MAY EXTEND WELL BEHIND THE ANAFRONT ACROSS THE CWA. WHILE
PRECIP COVERAGE SHOULD BE WINDING DOWN DURING THE EVENING,
PROFILES MAY COOL IN TIME TO OFFER A BRIEF PERIOD OF A WINTRY
MIX OR TRUE LIGHT SNOW SHOWERS. SOME MODEL SOUNDINGS SUGGEST
THAT BY THE TIME PROFILES COOL ENOUGH, WE MAY ONLY HAVE ENOUGH
LEFT IN THE TANK TO CHURN SOME FLURRIES.
MONDAY WILL BE THE COLDEST DAY OVER THE NEXT WEEK. MORNING LOWS
ARE FORECAST IN THE TEENS AND BLUSTERY CONDITIONS BEHIND THE
DEPARTING LOW MAY RESULT IN SUB-ZERO WIND CHILLS AREA-WIDE
MONDAY MORNING. AFTERNOON HIGHS ARE FORECAST IN THE 20S, BUT
WIND CHILLS MIGHT STAY IN THE SINGLE DIGITS ALL DAY LONG. UPPER
20S AND LOWER 30S ARE FAVORED IN THE DAYS TO FOLLOW. ENSEMBLE
GUIDANCE LIKES THE IDEA OF A CLIPPER SYSTEM IMPACTING THE UPPER
MIDWEST VIA SOME SNOW ON NEW YEAR'S EVE. THERE REMAINS A LOT OF
UNCERTAINTY IN WHAT THESE IMPACTS WILL ALL ENTAIL AND WHERE
THEY'LL BE FOUND. LATEST GUIDANCE FAVORS UP INTO WISCONSIN, BUT
THERE'S ENOUGH SUPPORT FOR A GLANCING BLOW LOCALLY TO KEEP AN
EYE ON THIS FOR POTENTIAL HOLIDAY TRAVEL IMPACTS.
DOOM
AVIATION /18Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 1204 PM CST WED DEC 24 2025
- A PERIOD OF SHOWERY DRIZZLE EXPECTED THIS EVENING/OVERNIGHT
PAIRED WITH IFR CIGS AND MVFR VSBYS (LIFR POSSIBLE AT GYY).
- MVFR TO POTENTIALLY IFR CIGS MAY PERSIST OR REDEVELOP DURING
THE DAY ON CHRISTMAS.
MVFR STRATUS WILL BEGIN TO LIFT INTO THE AREA FROM SOUTHWEST TO
NORTHEAST LATE AFTERNOON INTO EARLY EVENING (21-23Z). EXPECT A
PERIOD OF SHOWERY DRIZZLE TO THEN DEVELOP WITHIN AN HOUR OR TWO
OF THE MVFR STRATUS AS CIGS GRADUALLY LOWER TO IFR OVERNIGHT.
IFR CONDITIONS MAY BE MORE INTERMITTENT WITH NORTHWARD EXTENT,
WITH THE MORE PERSISTENT LOWER CIGS (POTENTIALLY LIFR) AT GYY.
VLIFR CIGS AND VSBYS ARE EXPECTED TO DEVELOP SOUTH OF I-80 AND
ACCORDINGLY SOUTH OF THE TERMINALS; HOWEVER, THE NORTHERN EDGE
OF THE VLIFR CONDITIONS WILL BE MONITORED CLOSELY IN CASE IT
ATTEMPTS TO LIFT FARTHER NORTH.
HEADING INTO THE DAYTIME HOURS ON CHRISTMAS DAY, THE INITIAL
IFR STRATUS LIKELY SCATTERS OUT OR LIFTS BACK TO MVFR EARLY IN
THE MORNING. THERE IS A SIGNAL FOR THIS LAYER TO THEN LOWER AND
THIN WITH TIME THROUGH THE MORNING WHICH COULD LEAD TO A RETURN
TO IFR IF THEY FAIL TO ERODE IN TIME.
SE WINDS THIS AFTERNOON WILL TURN LIGHT AND VARIABLE THIS
EVENING BEFORE SETTLING INTO A PREVAILING N TO NNE DIRECTION
LATE TONIGHT. SPEEDS THEN INCREASE DURING THE PRE-DAWN HOURS
THURSDAY OUT OF THE NE AROUND 10-12 KT WITH OCCASIONAL GUSTS
INTO THE UPPER TEENS THROUGH THE MORNING AS WINDS GRADUALLY VEER
ENE.
PETR
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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