597
FXUS63 KLOT 090257
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
857 PM CST SAT NOV 8 2025
KEY MESSAGES
- A STORM SYSTEM WILL BRING A PRECIPITATION THROUGH EARLY SUNDAY
MORNING. THE TRANSITION TO WET SNOW THAT HAS PUSHED INTO
NORTHWESTERN ILLINOIS WILL REACH AREAS NORTHWEST OF THE I-55
CORRIDOR AND INLAND FROM THE LAKE. THERE IS A (40-60%) CHANCE
FOR A SLUSHY INCH OR SO OF ACCUMULATION ACROSS NORTHWESTERN
IL, INCLUDING THE ROCKFORD AREA.
- LAKE EFFECT SNOW MAY MIGRATE FROM NORTHEASTERN ILLINOIS TO
NORTHWESTERN INDIANA SUNDAY MORNING AND INTO EARLY AFTERNOON,
WITH A LOW TO MEDIUM CHANCE (30-50%) FOR A QUICK INCH OR TWO
OF SNOW IN COOK, LAKE (IN), AND PORTER COUNTIES.
- INTENSE LAKE EFFECT SNOW BANDS MAY MOVE INTO PARTS OF
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA SUNDAY NIGHT
INTO MONDAY, MAKING FOR DANGEROUS TRAVEL. A WINTER STORM WATCH
IS IN EFFECT FOR COOK, EASTERN WILL, LAKE (IN), AND PORTER
COUNTIES.
- A GRADUAL WARMING TREND, POSSIBLY ACCOMPANIED BY PERIODS OF
BREEZY WINDS, IS EXPECTED TOWARD THE MIDDLE OF NEXT WEEK.
UPDATE
ISSUED AT 857 PM CST SAT NOV 8 2025
GOING FORECAST LOOKS RIGHT ON TRACK AND NO MEANINGFUL UPDATES OR
CHANGES PLANNED THIS EVENING. RAIN HAS BEGUN CHANGING TO SNOW
OVER OUR NORTHWESTERN CWA ALREADY AND THIS RAIN SNOW LINE SHOULD
SLOWLY PROGRESS SOUTHEASTWARD THROUGH THE NIGHT. TEMPS STILL
MOSTLY ABOVE FREEZING, BUT COULD FALL A DEGREE OR TWO TONIGHT,
LEADING TO SOME SLUSHY ACCUMULATION OF AN INCH OR SO, MAINLY ON
GRASSY AND ELEVATED SURFACES OVER NORTHWESTERN CWA.
AS COLD AIR ADVECTION RAMPS UP OVER THE LAKE LATE TONIGHT, LOOKS
LIKE A BAND OF HEAVIER LAKE EFFECT PRECIPITATION COULD DEVELOP
ALONG OR JUST INLAND OVER THE SOUTHWESTERN SHORE OF LAKE
MICHIGAN. TEMPS WILL PROBABLY BE COLD ENOUGH FOR SNOW BY THEN,
BUT PROBABLY JUST ABOVE FREEZING LIMITING THE THREAT OF
ACCUMULATIONS IF THE BAND WERE TO SLIP INLAND. IT'S GOING TO BE
CLOSE AND SOMETHING THE ONCOMING OVERNIGHT SHIFT WILL BE
MONITORING CLOSELY.
- IZZI
DISCUSSION
ISSUED AT 319 PM CST SAT NOV 8 2025
THROUGH MONDAY:
A STEADY SHIELD OF PRECIPITATION CONTINUES TO SLIDE EASTWARD
ACROSS IA IN ADVANCE OF A PAIR OF PHASING MID-LEVEL IMPULSES
ACROSS THE MID-MISSOURI VALLEY. THE EXPECTATION IS FOR THIS AREA
OF PRECIPITATION TO CONTINUE DEVELOPING EASTWARD INTO OUR AREA
THROUGH THE MID AND LATE AFTERNOON HOURS. WHILE A SEVERAL HOUR
HOUR PERIOD OF A STEADY SOAKING RAIN IS EXPECTED FOR MOST
THROUGH THE EVENING, A COOLING ATMOSPHERIC COLUMN ACROSS
NORTHWESTERN IL WILL SUPPORT A QUICK TRANSITION OVER TO WET SNOW
AFTER ABOUT 7 PM THIS EVENING ACROSS NORTHWESTERN SECTIONS OF
THE AREA (IN AND AROUND THE ROCKFORD AREA). ONCE THIS TRANSITION
OCCURS, THERE LOOKS TO BE ABOUT A 2 TO 3 HOUR PERIOD IN WHICH A
STEADY PERIOD OF SNOW WILL FALL MID TO LATE THIS EVENING. THIS
MAY RESULT IN SOME SNOW ACCUMULATIONS OF 1" TO POTENTIALLY 2" OF
WET SNOW ACROSS NORTHWESTERN SECTIONS OF IL, PRIMARILY ON
UNPAVED AND ELEVATED SURFACES DUE TO THE MARGINAL SURFACE
TEMPERATURES.
LATE TONIGHT INTO EARLY SUNDAY MORNING, DEEPENING LAKE INDUCED
INVERSION HEIGHTS WILL SUPPORT AN UPTICK IN LAKE EFFECT/LAKE
ENHANCED BANDS OF RAIN AND SNOW ALONG THE BACK SIDE OF THE
EXITING WEATHER SYSTEM. THIS LOOKS TO PARTICULARLY BE THE CASE
AROUND AND AFTER DAYBREAK SUNDAY MORNING FROM NEAR CHICAGO
SOUTHEAST INTO NORTHWESTERN IN. SURFACE TEMPERATURES LOOK TO
REMAIN MARGINAL (HOVERING AROUND OR A BIT ABOVE FREEZING) IN
THIS AREA DURING THIS TIME, SO THINKING IS THAT ANY ACCUMULATING
SNOW EARLY SUNDAY MORNING IN NORTHWESTERN IN WILL BE MORE
SLUSHY AND LIMITED TO NON-PAVED AND ELEVATED SURFACES.
FOLLOWING THE LINGERING MORNING ACTIVITY IN NORTHWESTERN IN,
THE FLOW OVER THE LAKE IS EXPECTED TO BACK NORTHWESTERLY, WHICH
SHOULD LARGELY PUSH ANY ADDITIONAL LAKE EFFECT ACTIVITY TO OUR
EAST SUNDAY AFTERNOON. ACCORDINGLY, ASIDE FROM SOME POSSIBLE
SCATTERED FLURRIES DURING THE DAY, IT APPEARS MUCH OF THE AREA
WILL GET A BREAK IN THE PRECIPITATION AS WE AWAIT OUR MORE
POTENTIALLY IMPACTFUL LAKE EFFECT SNOW EVENT SUNDAY NIGHT INTO
MONDAY.
CONCERNS CONTINUE TO INCREASE IN PERIODS OF HEAVY LAKE EFFECT
SNOW LATE SUNDAY NIGHT INTO MONDAY MORNING, WHICH COULD RESULT
IN AREAS OF VERY DANGEROUS, IF NOT IMPOSSIBLE, TRAVEL
CONDITIONS ACROSS PORTIONS OF THE CHICAGO METRO AREA INTO
FAR NORTHWESTERN IN INTO THE MONDAY MORNING COMMUTE. THE WORST
PERIOD LOOKS TO BE FROM AROUND MIDNIGHT SUNDAY NIGHT THROUGH
AROUND 10 AM MONDAY MORNING. THIS CONCERN HAS SHIFTED WEST OVER
THE PAST 24 HOURS TO INCLUDE THE IMMEDIATE CHICAGO AREA AND
POINTS SOUTHWARD NEAR AND ALONG THE IN STATE LINE. THIS WESTWARD
TREND IS LARGELY THE RESULT OF FORECAST GUIDANCE CONTINUING TO
FAVOR A FARTHER WESTWARD TRACK OF THE VIGOROUS POLAR WAVE
EXPECTED TO DIVE SOUTHWARD ACROSS THE WESTERN GREAT LAKES SUNDAY
NIGHT. THE GOING WINTER STORM WATCH HAS THIS AREA COVERED WELL.
THE ONLY CHANGE TO HEADLINES WAS TO ADD EASTERN WILL INTO THE
WATCH.
RECORD-COLD MID-LEVEL TEMPERATURES ACCOMPANYING THIS STRONG
WAVE (500MB TEMPERATURES OF -40C) WILL INDUCE EXTREME LAKE
INSTABILITY SUNDAY NIGHT (MARINE AIRMASS TO 700MB WATER
TEMPERATURE DIFFERENTIALS PUSHING 35C DEGREES WITH EFFECTIVE
EQUILIBRIUM LEVELS OF 22-25KFT). THESE REPRESENT SOME OF THE
MOST IMPRESSIVE LAKE EFFECT PARAMETERS I HAVE PERSONAL NOTED IN
MY 15 YEARS AT WFO LOT. CONSEQUENTLY, VERY INTENSE BANDS OF LAKE
EFFECT SNOW ARE POISED TO DEVELOP OVER LAKE MICHIGAN AND POINT
TOWARD THE SOUTHWESTERN LAKE MICHIGAN LAKESHORE SUNDAY NIGHT
INTO MONDAY.
ALL THINGS CONSIDERED, FEEL THERE CONTINUES TO BE AN INCREASING
SIGNAL FOR VERY IMPACTFUL LAKE EFFECT SNOW CHARACTERIZED BY
INTENSE SNOW RATES >2-3"/HR AND GUSTY NORTH WINDS >35 MPH TO
JUSTIFY THE THE CONTINUATION OF THE WINTER STORM WATCH FOR LAKE
AND PORTER COUNTIES IN NORTHWESTERN INDIANA AND COOK COUNTY IN
NORTHEASTERN ILLINOIS, AND ALSO TO ADD EASTERN WILL AS NOTED
ABOVE. ASSUMING FUTURE FORECAST TRENDS CONTINUE TO SUPPORT THIS
LAKE EFFECT SNOW INTO EASTERN IL AND NORTHWESTERN IN THE WINTER
STORM WATCH WILL LIKELY BE UPGRADED EITHER TONIGHT OR ON SUNDAY.
ALSO, WITH THE LAKE EFFECT BAND WILL LIKELY MAKE A FAR SOUTH-
SOUTHWESTERN INLAND PUSH AND CANNOT RULE OUT THE NEED FOR A
HEADLINE AS FAR INLAND AS KANKAKEE COUNTY. KEEP IN MIND THAT
LAKE EFFECT SNOW IS A HIGHLY LOCALIZED PHENOMENON AND CAN LEAD
TO VERY UNEQUAL IMPACTS. MUCH LIKE THUNDERSTORMS, LAKE EFFECT
SNOW CAN HAMMER A VERY LOCALIZED AREA WHILE KEEPING THE REST OF
A COUNTY RELATIVELY UNSCATHED. SO, BEING INCLUDED IN THE WINTER
STORM WATCH IS BY NO MEANS AN GUARANTEE WARNING-LEVEL IMPACTS
WILL BE FELT.
FINALLY, NOT TO BE FORGOTTEN, SUNDAY NIGHT WILL BE THE COLDEST
SO FAR THIS SEASON. THE COMBINATION OF OVERNIGHT LOWS IN THE 20S
AND BLUSTERY NORTH WINDS WILL DRIVE WIND CHILLS DOWN TOWARD THE
SINGLE DIGITS TO MID TEENS BY DAYBREAK MONDAY.
KJB/BORCHARDT
MONDAY NIGHT THROUGH SATURDAY:
LAKE EFFECT SNOW MAY STILL BE ONGOING ACROSS FAR NORTHEAST
PORTER COUNTY EARLY MONDAY EVENING, BUT IF IT IS, IT SHOULD
QUICKLY BE SHIFTING EAST AND THEN ENDING AS A RIDGE OF HIGH
PRESSURE RACES ACROSS THE CWA EARLY TUESDAY MORNING. WITH FAST
NORTHWEST FLOW ALOFT, A WEAK DISTURBANCE WILL MOVE SOUTHEAST
ACROSS THE WESTERN GREAT LAKES TUESDAY AFTERNOON. PRECIPITATION
AMOUNTS WITH THIS WAVE LOOK TO BE RATHER LIGHT, BUT PRECIP TYPES
ARE UNCERTAIN AND WILL BE BASED ON HOW FAST THE WARMER AIR
ARRIVES AND HOW SOON ANY POSSIBLE PRECIPITATION FALLS. A BIT
EARLY FOR ANY SPECIFICS, BUT A BRIEF LIGHT SNOW/SLEET MIX
QUICKLY CHANGING TO LIGHT RAIN/SPRINKLES LOOKS POSSIBLE.
TUESDAY AND WEDNESDAY LOOK POTENTIALLY WINDY WITH SOUTHWEST
WINDS GUSTING INTO THE 35 MPH RANGE TUESDAY AND WESTERLY WINDS
GUSTING INTO THE 30 MPH RANGE WEDNESDAY. DRY WEATHER IS EXPECTED
WEDNESDAY THROUGH NEXT SATURDAY ALONG WITH A WARMING TREND, WITH
HIGH TEMPS BACK INTO THE 50S FOR THE END OF NEXT WEEK AND
POSSIBLY INTO THE 60S NEXT SATURDAY. CMS
AVIATION /00Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 559 PM CST SAT NOV 8 2025
MAIN CONCERNS:
- RAIN MIXING WITH AND CHANGING TO WET SNOW TONIGHT INTO EARLY
SUNDAY, ACCOMPANIED BY MVFR TO IFR CONDITIONS. EXACT TIMING OF
CHANGEOVER REMAINS A BIT UNCERTAIN.
- ADDITIONAL SNOW SHOWERS OVER NORTHEAST IL AND NORTHWEST IN MAY
REDUCE VISIBILITY INTO THE DAYTIME HOURS OF SUNDAY AND AGAIN
SUNDAY EVENING.
- GUSTY NORTH-NORTHWEST WINDS (UP TO ~30 KT) ON SUNDAY.
LOW PRESSURE TRACKING ACROSS CENTRAL ILLINOIS WILL CONTINUE TO
SPREAD PRECIPITATION ACROSS THE REGION, INITIALLY RAIN, EVENTUALLY
MIXING WITH, AND THEN CHANGING TO SNOW, EARLIEST AT RFD. MOVED
THE MIXING AND CHANGEOVER TIMING A BIT LATER PER OBSERVATIONAL
AND RECENT GUIDANCE TRENDS. RFD MAY RECEIVE A SLUSHY ACCUM UP TO
1" ON COLDER SURFACES, WHILE ACCUMS ARE UNLIKELY AT THE CHICAGO
AREA TERMINALS. MADE OVERALL MINOR ADJUSTMENTS TO CIGS AND VSBY.
HAVE CONCERN FOR AN AREA OF FAIRLY ROBUST SNOW SHOWERS
FOLLOWING THE SYSTEM PRECIP THROUGH MID TO LATE SUNDAY MORNING
OVER THE CHICAGO METRO. ADJUSTED VSBY FOR THIS DOWN TO MVFR,
THOUGH IFR IS POSSIBLE, ESPECIALLY AT GYY DUE TO LAKE EFFECT.
TEMPS MAY STILL BE A BIT TOO MILD AND HIGHER SNOW RATES
INTERMITTENT ENOUGH TO PRECLUDE ANY REAL SNOW ACCUMS (BEST
CHANCE AGAIN PROBABLY AT GYY). LIGHTER SNOW SHOWERS SHOULD
PERSIST THE REST OF THE DAY AT GYY, WHILE ON AND OFF NON-
IMPACTFUL FLURRIES ARE POSSIBLE AT THE OTHER TAF SITES. SNOW
SHOWERS WILL REDEVELOP LATER SUNDAY EVENING OUT AHEAD OF WHAT
COULD BE INTENSE LAKE EFFECT SNOW MOVING ASHORE PRIMARILY AFTER
MIDNIGHT SUNDAY NIGHT (06Z MONDAY).
CURRENT EAST-NORTHEAST WINDS WILL STRENGTHEN AND BECOME
NORTHERLY OVERNIGHT, THEN NORTH-NORTHWESTERLY SUNDAY MORNING.
FORECAST SOUNDINGS SUPPORT FREQUENT GUSTS TO AROUND 30 KT AND
OCCASIONAL GUSTS UP TO 35 KT.
CASTRO
MARINE
ISSUED AT 315 PM CST SAT NOV 8 2025
AN AREA OF LOW PRESSURE WILL GRADUALLY DEEPEN TO 29.4 INCHES AS
IT MOVES EASTWARD FROM NORTHERN MISSOURI TO CENTRAL INDIANA ON
OVER THE NEXT 24 HOURS. ADDITIONALLY, HIGH PRESSURE OVER THE
NORTHERN PLAINS WILL INCREASE CREATING A STRONG PRESSURE
GRADIENT ORIENTED ACROSS LAKE MICHIGAN. AS A RESULT, NORTHERLY
WINDS WILL INCREASE QUICKLY THIS EVENING ALONG THE ILLINOIS
NEARSHORE OF LAKE MICHIGAN AND SPREAD TO THE INDIANA NEARSHORE
INTO SUNDAY MORNING. A PERIOD OF GALE FORCE WINDS TO 35 KT LOOK
LIKELY TO OCCUR DURING THE OVERNIGHT HOURS INTO SUNDAY MORNING,
BEFORE DIMINISHING SLIGHTLY IN THE AFTERNOON WITH OCCASIONAL
GUSTS TO 30 KNOTS. ANOTHER PERIOD OF GALE FORCE WINDS TO 35
KNOTS MAY OCCUR SUNDAY NIGHT INTO MONDAY MORNING AS A SECONDARY
SYSTEM MOVES SOUTHWARD DOWN LAKE MICHIGAN. FOR THESE REASONS,
THE GALE WATCH HAS BEEN UPGRADED TO A WARNING FROM MIDNIGHT
TONIGHT THROUGH 6 AM MONDAY FOR BOTH THE ILLINOIS AND INDIANA
NEARSHORE ZONES OF LAKE MICHIGAN.
BANDS OF LAKE EFFECT RAIN AND SNOW ARE EXPECTED TO DEVELOP
TONIGHT AND LAST THROUGH MONDAY ACROSS CENTRAL AND SOUTHERN LAKE
MICHIGAN. INTERMITTENT WATER SPOUTS MAY OCCUR IN THE MOST
INTENSE BANDS OF LAKE EFFECT RAIN AND SNOW.
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
MORNING FOR ILZ103-ILZ104-ILZ105-ILZ108.
IN...WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
AFTERNOON FOR INZ001-INZ002.
LM...GALE WARNING FROM MIDNIGHT TONIGHT TO 6 AM CST MONDAY FOR THE
IL NEARSHORE WATERS.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM CST SUNDAY
FOR THE IN NEARSHORE WATERS.
GALE WARNING FROM 6 AM SUNDAY TO 6 AM CST MONDAY FOR THE IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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