003
FXUS63 KLOT 090502
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1102 PM CST MON DEC 8 2025
KEY MESSAGES
- 30-60% CHANCES OF LIGHT SNOW MAINLY NORTHEAST OF A ROCKFORD
TO RENSSELAER LINE TONIGHT WITH A DUSTING OF SNOW ACCUMULATION
POSSIBLE. VERY LOW CHANCE (<20%) FOR FREEZING DRIZZLE LATE
TONIGHT INTO TUESDAY MORNING, ALSO ALONG/NORTH OF I-80.
- PERIOD OF LIGHT FREEZING RAIN LATE TUESDAY AFTERNOON INTO
EARLY TUESDAY EVENING, MAINLY NORTHWEST OF AN OTTAWA TO JOLIET
TO CHICAGO LINE, DURING THE EVENING RUSH HOUR.
- POSSIBLE SNOW SQUALLS WEDNESDAY MORNING.
- WINDY CONDITIONS TUESDAY NIGHT INTO WEDNESDAY WITH WIND GUSTS
TO 40 MPH POSSIBLE.
- MORE FAST MOVING CLIPPER SYSTEMS COULD RESULT IN SOME ADDITIONAL
PERIODS OF ACCUMULATING SNOW IN OUR NEAR OUR AREA LATE THIS WEEK
INTO THE WEEKEND.
- AFTER A BRIEF WARM-UP MIDWEEK, TEMPERATURES WILL TURN SHARPLY
COLDER DURING THE LATTER HALF OF THE WEEK. THE DEEP COLD MAY
ALSO RESULT IN SOME PERIODS OF DANGEROUS WIND CHILLS TO -20
THIS WEEKEND.
UPDATE
ISSUED AT 818 PM CST MON DEC 8 2025
THE FORECAST APPEARS TO BE IN GOOD SHAPE. MAIN SLIGHT CHANGE WAS
TO INCREASE SNOW CHANCES A BIT LATE TONIGHT MAINLY NEAR/NORTH OF
I-80.
AN AREA OF 10-20 DBZ RETURNS ON THE DVN RADAR IS CURRENTLY
VIRGA, WITH CLOUD BASES GENERALLY RUNNING ABOVE 9-10 KFT AND A
SIGNIFICANT DRY LAYER PRESENT BENEATH. AN 850-700 MB SHORTWAVE
TROUGH AXIS IS FORECAST TO PUSH EAST OF THE MISSISSIPPI RIVER
LATE THIS EVENING AND THEN ACROSS THE LOCAL FORECAST AREA
THROUGH MIDNIGHT TO 6 AM. DURING THIS TIMEFRAME, A SLIGHT
UPTICK IN 700 MB FRONTOGENESIS IS FORECAST TO TAKE SHAPE IN THE
VICINITY OF THE I-90 CORRIDOR. THE ASSOCIATED INCREASE IN LARGE
SCALE FORCING WILL RESULT IN A QUICK SATURATION OF THE
AFOREMENTIONED DRY LAYER, AND LIKELY ENOUGH TO SUPPORT THE
DEVELOPMENT OF AT LEAST FLURRIES ACROSS THE NORTHEAST 2/3RDS OF
THE CWA. ROUGHLY ALONG AND NORTHEAST OF A ROCKFORD TO RENSSELAER
LINE, HAVE INCREASED POPS A BIT GIVEN INDICATIONS THAT THIS
INCREASING ASCENT MAY ALLOW FOR SOME STEADIER (BUT STILL LIGHT)
SNOWFALL AS THE MAIN TROUGH AXIS PIVOTS OVERHEAD. ANY
ACCUMULATIONS LOOK LIKE THEY'LL REMAIN LIMITED TO A TENTH OR TWO
OR LESS OWING TO THE BRIEF NATURE (2 HOURS OR LESS) AND
GENERALLY MODEST NATURE OF THE INCOMING ASCENT. EXPECTING ANY
LIGHT SNOW TO BE PUSHING EAST OF OUR NW INDIANA LOCALES THROUGH
5-6 AM.
FINALLY, WHILE THE POTENTIAL FOR A LITTLE FREEZING DRIZZLE INTO
MID-MORNING TUESDAY REMAINS NON-ZERO, LATEST GUIDANCE CONTINUES
TO SUGGEST THIS POTENTIAL REMAINS LOW. WHILE MODELS MAINTAIN
ASCENT THROUGH THE LOW-LEVELS EARLY TUESDAY MORNING, FORECAST
SOUNDINGS REVEAL A BIT OF A MISMATCH BETWEEN THE ARRIVAL OF
LOWER CLOUD CEILINGS AND DEEPER SATURATION/CLOUD DEPTHS, WITH
THE LATTER RAPIDLY DIMINISHING THROUGH MID MORNING ON THE
BACKSIDE OF THE DEPARTING TROUGH. THIS RESULTS IN CLOUD DEPTHS
THAT REMAIN JUST A BIT TOO SHALLOW TO SUPPORT IMPACTFUL
DRIZZLE. HAVE CERTAINLY BEEN SURPRISED BY FZDZ SETUPS BEFORE
THOUGH, SO DON'T WANT TO ENTIRELY RULE OUT THE THREAT, JUST THAT
IT REMAINS LOW AND TOO LOW FOR AN INCLUSION IN THE GRIDDED
FORECAST GIVEN THE LATEST UPSTREAM OBSERVATIONS AND LATEST MODEL
OUTPUT.
AS DEWPOINTS INCREASE THROUGH THE UPPER 20S AND LOWER 30S
TOMORROW AFTERNOON, SOME MIST MAY DEVELOP AS THIS HIGHER-
MOISTURE AIRMASS PUSHES ACROSS OUR EXPANSIVE SNOWPACK.
CARLAW
DISCUSSION
ISSUED AT 145 PM CST MON DEC 8 2025
THROUGH WEDNESDAY:
THERE ARE MULTIPLE FORECAST CONCERNS/CHALLENGES THROUGH
WEDNESDAY AFTERNOON. THE LOCAL AREA WILL BE ON THE FAR SOUTHERN
END OF A CLIPPER SYSTEM MOVING ACROSS THE NORTHERN GREAT LAKES
TONIGHT WITH A CHANCE OF LIGHT SNOW OVERNIGHT, MAINLY NORTH OF
I-80. THERE MAY BE A DUSTING OF SNOW ACCUMULATION, ESPECIALLY
CLOSER TO THE IL/WI STATE LINE. THERE HAS ALSO BEEN THE CONCERN
FOR SOME PATCHY FREEZING DRIZZLE AS THIS LIGHT SNOW POTENTIAL
ENDS IN THE PREDAWN HOURS, WHICH THEN COULD PERSIST THROUGH
DAYBREAK. THE MOISTURE DEPTH LOOKS RATHER SHALLOW FOR FREEZING
DRIZZLE AND CONFIDENCE REMAINS TOO LOW TO INCLUDE IN THE
FORECAST BUT TRENDS WILL NEED TO BE MONITORED. THE GRADIENT
WILL ALSO TIGHTEN TONIGHT WITH SOUTHWEST WINDS GUSTING INTO THE
MIDDLE 20 MPH RANGE, WHICH WILL DIMINISH SOME ON TUESDAY.
THE NEXT FAST MOVING SYSTEM ARRIVES LATE TUESDAY AFTERNOON WITH
SOME LARGE CHANGES TO THE FORECAST. GIVEN HOW COLD THE GROUND
AND SNOW PACK IS, THERE REMAINS QUITE A BIT OF UNCERTAINTY FOR
HOW WARM TEMPS WILL RISE ON TUESDAY AND IF THEY MAY COOL AS
PRECIPITATION ARRIVES LATE IN THE AFTERNOON/EARLY EVENING. AS A
RESULT, STILL HAVE HIGH TEMPS GENERALLY IN THE MID 30S TUESDAY,
BUT THEN HAVE TEMPS FALLING BACK INTO THE LOWER 30S FOR A LARGE
AREA NORTHWEST OF AN OTTAWA/JOLIET/CHICAGO LINE. WHILE NOT A
CLASSIC FREEZING RAIN SET-UP, EVEN IF THE BULK OF THE
PRECIPITATION FALLING IS IN THE FORM OF LIQUID RAIN, LESS
TRAVELED SURFACES, SUCH AS SIDEWALKS, PARKING LOTS, ETC, MAY
STILL DEVELOP SOME ICING AND HAVE INCLUDED FREEZING RAIN IN THE
FORECAST FOR THESE AREAS. BOTH FROM A PRECIPITATION DURATION AND
FROM A TEMPERATURE PERSPECTIVE, THIS FREEZING RAIN POTENTIAL MAY
ONLY LAST A FEW HOURS. FOR THE REST OF THE AREA, AIR TEMPS
SLIGHTLY ABOVE FREEZING, SHOULD LIMIT FREEZING RAIN AND HAVE
CONTINUED WITH JUST LIQUID RAIN IN THE FORECAST. AND SINCE THIS
IS A LARGE CHANGE TO FORECAST, PLAN TO HOLD OFF ON AN ADVISORY
TO ALLOW TRENDS TO CONFIRM THESE CHANGES AS WELL AS WHERE THE
CUTOFF TO ANY POSSIBLE ADVISORY MAY BE NEEDED.
ALSO OF CONCERN IS ANY FURTHER SHIFT SOUTH TO THE TRACK OF THIS
SYSTEM, WHICH MAY POSSIBLY PUSH THE FREEZING RAIN POTENTIAL A
BIT FURTHER SOUTH, BUT MAY ALSO BRING MORE SNOW TO FAR NORTHERN
IL. FROM THIS DISTANCE, CONFIDENCE IS TOO LOW TO SAY WHERE THE
SOUTHERN EDGE OF THE SWATH OR SNOW WILL FALL AS JUST A SMALL
CHANGE TO THE TRACK OF THE SYSTEM COULD HAVE LARGE CHANGES TO
THE PRECIPITATION FORECAST.
AS THIS SYSTEM APPROACHES TUESDAY EVENING, SOUTHWEST WINDS WILL
STEADILY INCREASE AND THEN TURN MORE WESTERLY EARLY WEDNESDAY
MORNING. WIND GUSTS DURING THIS TIME PERIOD MAY REACH 40 MPH,
POSSIBLY HIGHER, WHICH THEN COULD LEAD FOR THE NEED FOR A
POSSIBLE WIND ADVISORY.
BY WEDNESDAY MORNING, THE TRUE COLD FRONT WILL MOVING ACROSS THE
AREA AND THIS LOOKS LIKE A GOOD SETUP FOR POSSIBLE SNOW SQUALLS,
WHICH THE HRRR AND NAMNEST ARE SHOWING WELL, WITH LOCALLY HIGHER
WIND GUSTS AND SIGNIFICANTLY REDUCED VISIBILITIES. THE OVERALL
TREND IN THE MODELS IS COLDER AND FASTER AND WHILE THERE IS
STILL A CHANCE OF RAIN WEDNESDAY MORNING ACROSS THE SOUTHEAST
CWA, ITS POSSIBLE THAT PRECIPITATION ENDS LATE TUESDAY NIGHT,
EARLY WEDNESDAY MORNING AND THEN THERE ARE SNOW SQUALLS IN THE
MORNING WITH LINGERING FLURRIES SNOW SHOWERS IN THE AFTERNOON.
WITH THESE TRENDS IN MIND, HAVE LOWERED TEMPS A FEW DEGREES
BOTH TUESDAY NIGHT AND ON WEDNESDAY. NORTHWEST WINDS WILL REMAIN
GUSTY WEDNESDAY AFTERNOON, BUT SHOULD BE SLOWLY DIMINISHING.
THE NORTHWEST WINDS WILL THEN LIKELY KEEP LAKE EFFECT SNOW
SHOWERS GOING ACROSS AT LEAST PORTER COUNTY IN NORTHWEST IN
WEDNESDAY AFTERNOON, WITH SOME MINOR SNOW ACCUMULATION
POSSIBLE. CMS
WEDNESDAY NIGHT THROUGH MONDAY:
AN ACTIVE BELT OF STRONG NORTHWESTERLY UPPER-LEVEL FLOW IS
ANTICIPATED TO PERSIST FROM THE NORTHERN PLAINS SOUTHEASTWARD
ACROSS THE LOWER GREAT LAKES THROUGH MUCH OF THE PERIOD. THIS
WILL STEER AT LEAST 2 TO 3 ADDITIONAL CLIPPER TYPE IMPULSES
SOUTHEASTWARD ACROSS OUR GENERAL REGION THURSDAY AND INTO THE
WEEKEND, WITH EACH ONE COMING WITH CHANCES OF ACCUMULATING
SNOWFALL IN OUR VERY NEAR OUR AREA. WITH THAT BEING SAID, THERE
STILL CONTINUES TO BE LITTLE CONSISTENCY IN ENSEMBLE GUIDANCE
REGARDING THE EXACT TRACKS, TIMING, AND STRENGTH OF EACH OF
THESE WEATHER IMPULSES. ACCORDINGLY, WHILE THE CHANCE OF MORE
SNOW NEAR THE AREA REMAINS ELEVATED (ABOVE 50%), CONFIDENCE
REMAINS LOW WITH THE FINER-SCALE DETAILS OF THE FORECAST (SUCH
AS THE EXACT TIMING AND WHICH EXACT AREAS ARE THE MOST FAVORED)
LATER THIS WEEK THROUGH THE WEEKEND.
CONFIDENCE REMAINS HIGH THAT TEMPERATURES WILL TURN SHARPLY
COLDER FOR THE WEEKEND AS ANOTHER ARCTIC AIRMASS ENGULFS MUCH OF
THE MIDWEST AND GREAT LAKES REGION. THE ENSEMBLE SIGNAL FOR
THIS REMAINS STRONG, AND CURRENT INDICATIONS CONTINUE TO
GENERALLY SUPPORT UPPER SINGLE DIGIT TO TEENS HIGH TEMPERATURES
AND OVERNIGHT LOWS AT OR BELOW ZERO IN MOST LOCATIONS FOR THE
WEEKEND. MOST CONCERNING AT THIS POINT IS THE POTENTIAL FOR A
PERIOD OF BLUSTERY NORTHWESTERLY WINDS TO ACCOMPANY THIS DEEP
COLD OVER THE WEEKEND, WHICH COULD RESULT IN SOME PERIODS OF
DANGEROUS WIND CHILLS NEARING -20F.
KJB
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1102 PM CST MON DEC 8 2025
MID-LEVEL VFR STRATUS CURRENTLY SHIFTING EASTWARD ACROSS
NORTHERN ILLINOIS WILL GRADUALLY LOWER INTO LOW-END MVFR LEVELS
BY SUNRISE. A NARROW BUT PROMINENT N/S AXIS OF ASCENT WITHIN THE
LOWERING STRATUS IS PRODUCING A DEVELOPING RIBBON OF SN OVER
NORTHERN ILLINOIS, WITH EACH SITE LIKELY OBSERVING A BRIEF 1-2
HOUR PERIOD OF IFR OR LOW-END MVFR VISIBILITY THROUGH 10Z. A
QUICKLY LOWERING INVERSION WILL GREATLY DECREASE CLOUD DEPTHS
AND LIKELY END PRECIP IN THE PRE-DAWN HOURS. HOWEVER, CANNOT
FULLY RULE OUT A BRIEF PERIOD OF FZDZ IN THE 10-12Z WINDOW
BEFORE CLOUD DEPTHS DECREASE FURTHER.
IT IS EXPECTED THAT LOW-END MVFR TO HIGH-END IFR STRATUS WILL
PERSIST THROUGH THE DAY UNDER THE LOWERING AND STRENGTHENING
INVERSION. CEILINGS MAY LOWER SOLIDLY INTO IFR LEVELS THROUGH
THE DAY AS LOW-LEVEL MOISTURE ADVECTION COUNTERS DIURNAL
PROCESSES. LIFR CEILINGS MAY ALSO REACH AS FAR SOUTHEAST AS RFD
DURING THE AFTERNOON. WITH THAT SAID, THE EXPECTED SHALLOW
NATURE OF THE STATUS ALSO MEANS IT WILL BE PRONE TO MIXING OUT
FROM SOUTHWEST TO NORTHEAST, WITH FEW/SCT CLOUDS POSSIBLE AT
MOST SITES LATER IN THE DAY.
AN IMPRESSIVE SURGE OF LOW-LEVEL MOISTURE ADVECTION WITH A
50-60 KNOT LOW-LEVEL JET THIS EVENING WILL PROMOTE A BAND OF
PRECIP ACROSS ALL TERMINALS THROUGH THE EVENING HOURS. WHILE RA
IS FAVORED THROUGH THIS PERIOD, EVAPORATIVE COOLING OF THE
OVERALL WARMING ENVIRONMENT MAY YIELD A 1-2 HOUR PERIOD OF PL
AND/OR SN AT THE ONSET OF PRECIP. STRONG COLD-AIR ADVECTION LATE
TONIGHT WILL LIFT CEILINGS INTO VFR LEVELS, BUT ALSO GENERATE
ISOLATED SNOW SHOWERS OR FLURRIES PRIOR TO SUNRISE.
EXPECT SW/SSW WINDS AROUND 10 KNOTS TO INCREASE WITH GUSTS OVER
20 KNOTS THROUGH THE EARLY MORNING HOURS, WITH LLWS WHENEVER
GUSTS ARE NOT PRESENT. GUSTS OVER 20 KNOTS WILL BE COMMON
THROUGH THE DAY, FOLLOWED BY GUSTS OVER 25 KNOTS IN RESPONSE TO
THE STRONG LOW-LEVEL JET THIS EVENING. WINDS WILL THEN VEER
WSW/W WITH GUSTS TO 35 KNOTS BEHIND THE COLD FRONT LATE
TONIGHT.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL NOON CST TUESDAY FOR WINTHROP
HARBOR IL TO GARY IN.
GALE WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY AFTERNOON
FOR THE IL AND IN NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 3 PM CST TUESDAY FOR GARY TO BURNS
HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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