521
FXUS63 KLOT 101212
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
612 AM CST SAT JAN 10 2026
KEY MESSAGES
- A PERIOD OF RAIN AND SNOW IS EXPECTED THIS MORNING. SOME
WET/SLUSHY SNOW ACCUMULATIONS ARE POSSIBLE MAINLY NEAR AND
NORTH OF A ROCHELLE TO WAUKEGAN LINE.
- CONTINUING TO MONITOR A THREAT FOR ROBUST, WIND-WHIPPED SNOW
SHOWERS AND/OR SQUALLS THIS EVENING WHICH MAY LEAD TO QUICK
SNOW ACCUMULATIONS AND SHARPLY-REDUCED VISIBILITIES,
ESPECIALLY SOUTH OF I-80.
- UP AND THEN DOWN TEMPERATURES NEXT WEEK WITH OCCASIONAL
OPPORTUNITIES FOR (MAINLY LIGHT) PRECIPITATION.
DISCUSSION
ISSUED AT 346 AM CST SAT JAN 10 2026
THROUGH SUNDAY:
FOCUS IN THE NEAR TERM IS ON AN ACTIVE PERIOD OF WEATHER THIS
MORNING THROUGH ABOUT MIDDAY SUNDAY. SNOW/RAIN WITH SOME SLUSHY
ACCUMS THIS MORNING WILL GIVE WAY TO BLUSTERY AND COLDER
CONDITIONS LATER TODAY, WITH SCATTERED CONVECTIVE SNOW
SHOWERS/SQUALLS POSSIBLE TONIGHT. SNOW SHOWERS WILL TAPER TO
FLURRIES SUNDAY MORNING EXCEPT FOR NORTHEAST PORTER COUNTY IN
WHERE LAKE EFFECT SNOW SHOWERS WILL LINGER, BEFORE CONDITIONS
IMPROVE SUNDAY AFTERNOON.
LOW-LEVEL STRATUS, WHICH LINGERED ACROSS THE SOUTHERN PARTS OF
THE CWA LATE FRIDAY HAS EXPANDED IN COVERAGE OVERNIGHT, WHICH
ALONG WITH INCREASING MID/HIGH LEVEL CLOUD COVER HAS KEPT
TEMPERATURES RELATIVELY MILD FROM THE MID-30S TO AROUND 40
DEGREES ACROSS THE FORECAST AREA. REGIONAL RADAR MOSAIC DEPICTS
PRECIPITATION DEVELOPING FROM MO/IA EAST-NORTHEASTWARD INTO
WESTERN IL AT THIS HOUR, IN ASSOCIATION WITH AN APPROACHING
PHASING AND DEEPENING MID-LEVEL SHORT WAVE TROUGH. GIVEN THE
RELATIVELY MILD SURFACE TEMPS (AND DEW POINT/WETBULB TEMPS),
THIS PRECIPITATION IS EXPECTED TO BEGIN AS RAIN BUT EVENTUALLY
MIX WITH/CHANGE TO WET SNOW AS STRENGTHENING ASCENT DYNAMICALLY
COOLS THE COLUMN. A COMBINATION OF STEEP MID-LEVEL LAPSE RATES
(> 7 C/KM ABOVE ABOUT 650 MB) AND A PERIOD OF RELATIVELY STRONG
ASCENT WITHIN THE DGZ SHOULD SUPPORT DECENT PRECIPITATION
RATES, THOUGH THE INITIALLY MILD BOUNDARY LAYER TEMPS AND WARM
GROUND CONDITIONS WILL LIKELY MODULATE SURFACE SNOW ACCUMULATION
TO SOME DEGREE.
MODEL THERMAL FIELDS SUGGEST AREAS NORTHWEST OF ABOUT A ROCHELLE
TO WAUKEGAN LINE ARE MOST LIKELY TO SEE A PERIOD OF ALL WET
SNOW DEVELOP AND PERSIST THROUGH MID-LATE MORNING, BEFORE
PRECIPITATION TAPERS OFF WITH THE PASSAGE OF THE INITIAL VORT
AXIS EASTWARD SHIFT OF THE LOW-LEVEL FRONT/BAROCLINIC ZONE.
THE AFOREMENTIONED AREAS WILL THUS HAVE THE GREATEST CHANCE OF
SEEING SLUSHY ACCUMS OF AROUND 1" TO PERHAPS LOCALLY 2" BY LATE
MORNING, WITH LITTLE OR NO SIGNIFICANT ACCUMS FARTHER
SOUTH/SOUTHEAST FROM THERE. AS INDICATED ABOVE, PRECIPITATION
SHOULD LARGELY COME TO AN END FROM WEST-EAST BY MIDDAY/EARLY
AFTERNOON.
WINDS WILL BECOME BLUSTERY FROM THE WEST THIS AFTERNOON (GUSTS
NEAR 30 MPH), AS SURFACE LOW PRESSURE CONSOLIDATES EAST OF US
ACROSS THE GREAT LAKES/UPPER OHIO VALLEY. COLDER AIR BOTH
SURFACE AND ALOFT WILL ADVECT INTO THE REGION, AS ANOTHER STRONG
MID-LEVEL VORT DIGS INTO THE DEEPENING TROUGH FROM THE
NORTHWEST. THIS IS EXPECTED TO STEEPEN LOW-LEVEL LAPSE RATES AND
GRADUALLY DEEPEN THE BOUNDARY LAYER LATE THIS AFTERNOON INTO
THIS EVENING, LEADING TO THE DEVELOPMENT OF SCATTERED CONVECTIVE
SNOW SHOWERS AND POTENTIALLY SNOW SQUALLS (RAP SNOW SQUALL
PARAMETER, WHICH COMBINES LOW-LEVEL LAPSE RATES, RH AND MEAN
WINDS, DOES SUPPORT SQUALLS). HIGH-RES GUIDANCE SEEMS TO FOCUS
THE GREATEST COVERAGE ACROSS OUR SOUTHERN CWA/CENTRAL IL THIS
EVENING, BUT WILL HAVE TO KEEP AN EYE ON THE POTENTIAL FOR
SCATTERED GUSTY SNOW SHOWERS CAPABLE OF REDUCING VISIBILITIES
AND PRODUCING LOCALIZED LIGHT (INCH OR LESS) ACCUMULATIONS
ACROSS THE AREA TONIGHT. PERHAPS A LIMITING FACTOR FOR ORGANIZED
SNOW SQUALL CONDITIONS IS THAT THESE WILL BE OCCURRING IN A
BROAD REGION OF LOW-LEVEL COLD ADVECTION WITHOUT A FRONTAL ZONE
TO FOCUS LOW- LEVEL CONVERGENCE. EVEN OUTSIDE OF SNOW SHOWERS,
WINDS GUSTING 30-35 MPH AT TIMES, TEMPERATURES FALLING INTO THE
LOW-MID 20S AND WIND CHILLS IN THE SINGLE DIGITS TO NEAR 10
ABOVE WILL MAKE FOR A BLUSTERY NIGHT.
SNOW SHOWERS SHOULD TAPER OFF TO SCATTERED FLURRIES BY SUNDAY
MORNING, THOUGH SCATTERED LAKE EFFECT SNOW SHOWERS ARE POSSIBLE
ACROSS NORTHEAST PORTER COUNTY THROUGH ABOUT MIDDAY. A LOWERING
SUBSIDENCE INVERSION WILL PROVIDE DECREASING CLOUD COVER AND
DIMINISHING WINDS THROUGH THE AFTERNOON WITH SEASONABLE
TEMPERATURES IN THE LOW-30S.
RATZER
SUNDAY NIGHT THROUGH FRIDAY:
ANOMALOUSLY STRONG MID-UPPER RIDGING WILL ESTABLISH NEAR THE
PACIFIC COAST THROUGH NEXT WEEK, RESULTING IN A PREDOMINANTLY
NORTHWESTERLY FLOW PATTERN FOR THE EASTERN 2/3 OF NORTH AMERICA.
SEASONABLE CONDITIONS ON SUNDAY EVENING WILL GIVE WAY TO A FEW
DAYS OF SOLIDLY ABOVE NORMAL TEMPS (THROUGH TUESDAY EVENING),
FOLLOWED BY A RETURN TO MORE SEASONABLE READINGS FOR MID JANUARY
THROUGH THE REST OF THE WEEK. THERE WILL BE OCCASIONAL
OPPORTUNITIES FOR PRECIPITATION, THOUGH THE DEEP NORTHWEST FLOW
PATTERN WILL BE UNFAVORABLE FOR ANY MOISTURE LADEN SYSTEMS.
FOLLOWING AN EVENING DIP IN TEMPS SUNDAY EVENING (~20-25F),
STRONG 1035 MB HIGH PRESSURE WILL SETTLE INTO THE MID SOUTH. IN
RESPONSE, AS A FAIRLY ROBUST LOW-LEVEL JET SHIFTS OVERHEAD, A
COMMENSURATE INCREASE IN SOUTHWEST WINDS WILL RESULT IN RISING
TEMPERATURES OVERNIGHT INTO EARLY MONDAY.
WITH THE FIRST IN A SERIES OF CLIPPER-TYPE SYSTEMS PASSING WELL TO
THE NORTH MONDAY INTO TUESDAY, THE BREEZY WARM ADVECTION REGIME
WILL RESULT IN HIGHS IN THE LOWER TO MID 40S MONDAY, NEAR TO A
BIT ABOVE FREEZING LOWS MONDAY NIGHT, AND THEN HIGHS INTO THE
UPPER 40S TO AROUND 50F ON TUESDAY. SOME SPOTTY LIGHT RAIN
SHOWERS OR JUST SPRINKLES ARE POSSIBLE ON TUESDAY INTO THE
EARLY EVENING. THE COLD FRONT TRAILING FROM LOW PRESSURE
PASSING THROUGH OR JUST NORTH OF THE NORTHERN GREAT LAKES WILL
THEN SHIFT ACROSS THE AREA BY THE EVENING, BRINGING THE EARLY
WORKWEEK STRETCH OF MILD TEMPS TO AN END.
MID-UPPER TROUGHING WILL DEEPEN OVER THE EASTERN US ON WEDNESDAY
AS A FEW EMBEDDED SHORT-WAVE IMPULSES PRESS SOUTHEASTWARD. THE
COLD ADVECTION REGIME ON WEDNESDAY SHOULD SUPPORT AT LEAST
SCATTERED SNOW SHOWERS (30-50% POPS FOR NOW ARE REASONABLE),
THOUGH MARGINAL SURFACE TEMPS TO START THE DAY AND SHOWERY NATURE
OF THE SNOW SHOULD TEND TO LIMIT ACCUMULATION/IMPACT POTENTIAL.
WITH THE MOST ROBUST MID-LEVEL HEIGHT FALLS CONFINED TO THE
MORNING THROUGH MIDDAY, SNOW SHOWER COVERAGE AND/OR INTENSITY
MAY TEND TO DIMINISH INTO THE AFTERNOON.
WE'LL THEN NEED TO WATCH FOR A WINDOW OF FAVORABLE LAKE EFFECT
THERMODYNAMICS WEDNESDAY NIGHT INTO PRE-DAWN THURSDAY (IF
FORECAST MID-LEVEL SUBSIDENCE IS NOT TOO DELETERIOUS),
SUPPORTING ~30-40% CHANCE POPS FOR PORTIONS OF NORTHEAST IL AND
NORTHWEST IN. ANY BREAK FOLLOWING THE POSSIBLE LAKE EFFECT SNOW
SHOWERS WILL BE SHORT-LIVED, WITH SIGNS POINTING TOWARD AN
ADDITIONAL CLIPPER SYSTEM OR TWO AFFECTING THE REGION SOMETIME
IN THE THURSDAY PM-SATURDAY TIMEFRAME. SOME GUIDANCE MEMBERS
SUGGEST THE CLIPPER SHORT-WAVE COULD TEMPORARILY BECOME A CUT-
OFF LOW INTO THE START OF THE WEEKEND. IF THIS COMES TO PASS,
WARM ADVECTION DRIVEN SNOW LATE THURSDAY PM-THURSDAY NIGHT WOULD
BE FOLLOWED BY ON AND OFF SNOW SHOWERS FRIDAY INTO SATURDAY.
CASTRO
AVIATION /12Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 612 AM CST SAT JAN 10 2026
MAIN CONCERNS:
- RAIN TO WET SNOW THIS MORNING WITH RUNWAY ACCUMS UNLIKELY,
ACCOMPANIED BY 1-5SM VSBY.
- MVFR TO IFR CIGS THROUGH MIDDAY/EARLY AFTERNOON AND THEN
TEMPORARY MVFR CIGS WITH SNOW SHOWERS TONIGHT INTO SUNDAY.
- WIND-WHIPPED SNOW SHOWERS POSSIBLE THIS EVENING AND AGAIN
EARLY SUNDAY.
WITH PRECIPITATION OVERSPREADING THE REGION THIS MORNING, WELL
ABOVE FREEZING AIR TEMPERATURES OVER THE CHICAGO METRO CAST
UNCERTAINTY REGARDING THE EXACT TIMING FOR PRECIP TYPE TO MIX
WITH AND POSSIBLY CHANGE TO SNOW. IN ADDITION, RUNWAY AND
TAXIWAY ACCUMULATIONS APPEAR UNLIKELY. RFD FINALLY MIXED WITH
SNOW AS OF THIS WRITING COINCIDENT WITH A WIND SHIFT TO
WESTERLY. OTHERWISE DIDN'T MAKE BIG CHANGES TO PREVIOUS
ISSUANCES REGARDING CIG AND VSBY EXPECTATIONS INTO EARLY THIS
AFTERNOON, WITH VSBY AS LOW AS 1-2SM STILL INDICATED. IT DOES
APPEAR SNOW SHOWERS AND BR ON THE BACKSIDE OF THE STEADY PRECIP
WILL TAKE A BIT LONGER TO CLEAR THE TERMINALS. AS THIS OCCURS,
WEST-NORTHWEST WINDS WILL MORE MARKEDLY INCREASE, WITH GUSTS UP
INTO THE MID 20S KTS AND CIGS LIFTING/SCATTERING.
MULTIPLE DISTURBANCES MOVING OVERHEAD SHOULD RESULT IN THE
DEVELOPMENT OF SCATTERED WIND-WHIPPED SNOW SHOWERS AND FLURRIES
TONIGHT INTO SUNDAY MORNING. THERE'S A NON-ZERO CHANCE FOR SNOW
SQUALLS THIS EVENING, THOUGH HIGHER CHANCES MAY FOCUS SOUTH OF
THE TERMINALS. FOR THE EARLY SUNDAY MORNING POTENTIAL, FORECAST
SOUNDINGS SUGGEST GUSTS COULD APPROACH 35 KT. OPTED TO MAINTAIN
THE EVENING PROB30 FOR IFR SNOW SHOWERS, WITH A SLIGHTLY LATER
TIMING, AND ADDED ANOTHER IFR SNOW SHOWERS PROB30 FOR THE
CHICAGO METRO TAF SITES IN THE PRE-DAWN HOURS OF SUNDAY.
TEMPERATURES WILL BE COLD ENOUGH THAT ANY SUFFICIENTLY LONG
DURATION OF HIGHER SNOW RATES TONIGHT INTO SUNDAY MORNING COULD
RESULT IN A COATING OF SNOW ON PAVEMENT.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 3 PM CST
SUNDAY FOR WINTHROP HARBOR IL TO GARY IN.
SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 3 AM CST
SUNDAY FOR GARY TO BURNS HARBOR IN-BURNS HARBOR TO
MICHIGAN CITY IN.
SMALL CRAFT ADVISORY FROM NOON SUNDAY TO MIDNIGHT CST SUNDAY
NIGHT FOR GARY TO BURNS HARBOR IN-BURNS HARBOR TO
MICHIGAN CITY IN.
GALE WARNING FROM 3 AM TO NOON CST SUNDAY FOR GARY TO BURNS
HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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