612
FOUS11 KWBC 121847
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
147 PM EST FRI DEC 12 2025
VALID 00Z SAT DEC 13 2025 - 00Z TUE DEC 16 2025
..MONTANA
DAY 1...
THE ONGOING STRONG UPPER JET STREAK ANGLED NW TO SE WILL CONTINUE
TONIGHT AND INTO EARLY SATURDAY, WHILE WESTERLY MID-LEVEL FLOW
ISENTROPICALLY ASCENDS THE BAROCLINIC GRADIENT LEFT FROM A COLD
FRONT BANKED AGAINST THE CONTINENTAL DIVIDE. THIS WILL RESULT IN
PERSISTENT MODERATE SNOWFALL WITH RATES 0.5"/HR TO 1"/HR AT TIMES
ACROSS CENTRAL MT. THE HEAVIEST SNOWFALL SHOULD TAPER OFF QUICKLY
LATE TONIGHT WITH SNOW ENDING BY SATURDAY MORNING IN RESPONSE TO
THE STRONGEST ASCENT PIVOTING EAST AWAY FROM THE AREA. THE
CONTINUING SNOWFALL SHOULD REMAIN FLUFFY WITH HIGH SLRS THANKS TO A
VERY COLD COLUMN, SO ADDITIONAL ACCUMULATIONS EXCEEDING 4 INCHES
ARE LIKELY (>70% CHANCE) IN CENTRAL MT, WITH LOCAL ADDITIONAL
SNOWFALL AS MUCH AS 8 INCHES POSSIBLE (10% CHANCE) IN A FEW AREAS.
...NORTHERN PLAINS THROUGH THE OHIO VALLEY INTO THE CENTRAL
APPALACHIANS...
DAYS 1-2...
A CLOSED 500MB LOW DROPPING ALONG THE ONTARIO/GREAT LAKES BORDER
WILL BE THE CATALYST FOR ANOTHER FAST MOVING CLIPPER-TYPE LOW
RACING FROM THE NORTHERN PLAINS TO THE OHIO VALLEY D1, AND THEN
EXITING THE MID-ATLANTIC COAST D2. THE PRIMARY DRIVER OF THIS
CLIPPER IS EXPECTED TO BE A SECONDARY IMPULSE/VORTICITY LOBE
SWINGING THROUGH THE PINCHED FLOW, TO COMBINE WITH THE PERSISTENT
AND INTENSE UPPER JET STREAK ALOFT DRIVING DEEP LAYER ASCENT. WHILE
THE TEMPORAL DURATION OF ANY LIFT WILL BE MODEST DUE TO THE
PROGRESSIVE NATURE OF THE SYSTEM, THE OVERLAP OF HEIGHT FALLS WITH
INTENSIFYING FGEN (BOTH THROUGH WAA AND THE RESULT OF THE UPPER JET
STREAK POSITION) WILL BE SUFFICIENT TO DRIVE ROBUST OMEGA THROUGH
THE SNOW GROWTH ZONE. WITH STRONG LIFT OCCURRING INTO A DGZ THAT IS
DEEPENING IN THE COLD AIRMASS, PERIODS OF HEAVY SNOW ARE LIKELY,
ESPECIALLY WITHIN A NARROW TRANSLATING BAND FROM EASTERN SD THROUGH
IN ON D1, AND THEN CONTINUING INTO OH D2 BEFORE RUNNING INTO THE
TERRAIN OF WV AND WRINGING OUT THE REMAINING MOISTURE VIA UPSLOPE
ENHANCEMENT BEFORE SATURDAY NIGHT.
WPC PROBABILITIES FOR SNOW EXCEEDING 4" REACHES 10-30% FROM EASTERN
SD THROUGH CENTRAL IN, BUT CONTAINS A LOCAL MAXIMA ABOVE 50% IN
CENTRAL IL/IN WHERE THE BEST OVERLAP OF ASCENT INTO THE DEEPENING
DGZ OCCURS. THIS COULD SUPPORT SNOWFALL RATES ABOVE 1"/HR AT TIMES
LEADING TO LOCAL MAXIMA ABOVE 6" (10% CHANCE). DURING D2 THE
HEAVIEST SNOWFALL AXIS SHIFTS EASTWARD, WITH A 50-90% CHANCE OF
MORE THAN 4 INCHES OCCURRING ACROSS SOUTHERN OH AND INTO THE
TERRAIN FROM THE LAUREL HIGHLANDS OF PA THROUGH CENTRAL WV. THE
GREATEST SNOWFALL, WHICH MAY REACH 10" IN LOCAL SPOTS, IS EXPECTED
IN THE HIGHER TERRAIN OF WV.
..MID-ATLANTIC THROUGH SOUTHERN NEW ENGLAND
DAY 2...
EXTREMELY CHALLENGING FORECAST FOR SUNDAY AS A SYSTEM DEVELOPS EAST
OF THE MID-ATLANTIC SUNDAY MORNING AND THEN SKIRTS OFF INTO THE
ATLANTIC OCEAN. THE PRIMARY MECHANISM FOR THIS SYSTEM WILL BE THE
UPSTREAM SHORTWAVE RACING ACROSS THE MIDWEST. AS THIS FEATURE MOVES
EAST, IT WILL AMPLIFY RAPIDLY INTO A SHARPENING TROUGH, BUT STILL
MAINTAIN A POSITIVE TILT. DOWNSTREAM OF THIS TROUGH, ESPECIALLY 06Z
TO 18Z SUNDAY, RAPID HEIGHT FALLS WILL OCCUR THROUGH THE MID-
ATLANTIC STATES AND INTO SOUTHERN NEW ENGLAND, CONCURRENT WITH A
RAPID AMPLIFICATION OF A JET STREAK WHICH PEAK ABOVE 150 KTS IN NEW
ENGLAND WHILE ARCING MORE POLEWARD. THIS WILL PLACE THE FAVORABLE
RRQ FOR DIFFLUENT ASCENT DIRECTLY BENEATH THE STRONGEST HEIGHT
FALLS, AND THE ACCOMPANYING (ALBEIT MODEST) FGEN DUE TO WAA WILL
MERGE WITH THE RESULTING FGEN FROM THE JET STREAK TO DRIVE A PERIOD
OF RAPIDLY INTENSIFYING DEEP LAYER ASCENT. THE GUIDANCE CONTINUES
TO SUGGEST THAT THE STRONGEST LIFT WILL OCCUR DIRECTLY INTO THE
DGZ, SO DESPITE MARGINAL THERMALS AT ONSET (ESPECIALLY ACROSS THE
MID-ATLANTIC) PRECIPITATION WILL BECOME INCREASINGLY ALL-SNOW, AND
MAY BE HEAVY AT TIMES AS BANDED SNOW DEVELOPS AND PIVOTS NORTHEAST.
THIS EVENT SHOULD LAST NO MORE THAN 12 HOURS IN ANY GIVEN LOCATION,
AND THE EXACT PLACEMENT, TIMING, AND INTENSITY OF THE JET STREAK
WILL CREATE THE IMPORTANT DIFFERENCES IN SNOWFALL PLACEMENT AND
AMOUNTS. WHILE GUIDANCE CONTINUES TO FEATURE SOME DIFFERENCES,
THERE HAS BEEN A REDUCTION IN SPREAD THIS AFTN WHICH IS REFLECTED
BY INCREASING PROBABILITIES FOR ACCUMULATING SNOWFALL, ESPECIALLY
ALONG THE I-95 CORRIDOR FROM WASHINGTON, D.C. TO NYC. AT THIS TIME,
WPC PROBABILITIES SUGGEST A 30-70% CHANCE OF AT LEAST 2 INCHES FROM
WASHINGTON TO NY AND ONTO CAPE COD, WITH THE GREATEST POTENTIAL FOR
4+ INCHES OCCURRING FROM NEAR PHILADELPHIA THROUGH CENTRAL LONG
ISLAND. WHILE THIS WILL OCCUR EARLY SUNDAY MORNING, AT LEAST
BRIEFLY HEAVY SNOWFALL RATES WILL MAKE FOR HAZARDOUS TRAVEL.
..GREAT LAKES
DAYS 1-3...
PERSISTENT TROUGHING ACROSS THE EAST WILL MAINTAIN COLD
CONDITIONS, WITH MULTIPLE SHORTWAVES AND ACCOMPANYING COLD FRONT
DRIVING RENEWED CAA FOR LAKE EFFECT SNOW (LES) WITH MODEST SYNOPTIC
SNOW ALSO ACCOMPANYING EACH IMPULSE. THESE IMPULSES ARE MOST LIKELY
TO CROSS THE REGION ON SATURDAY, WITH ANOTHER IMPULSE ON MONDAY.
WHILE THE ACCOMPANYING SYNOPTIC/WAA SNOW IS LIKELY TO PRODUCE ONLY
MODEST ACCUMULATIONS, THE POST-FRONTAL CAA WILL CAUSE 850MB TEMPS
TO DROP TO AS LOW AS -20C TO -25C SAT/SUN, WITH MORE TEMPERED COLD
OF AROUND -10C MONDAY. WHILE THE HEAVIEST LES IS EXPECTED
SATURDAY/SUNDAY AS INVERSION DEPTHS OVER THE LAKES CLIMB TOWARDS
10,000 FT, SIGNIFICANT LES IS ALSO LIKELY MONDAY DESPITE THE WEAKER
OVERALL ASCENT/LAKE-INDUCED INSTABILITY.
WPC PROBABILITIES D1 AND D2 ARE ELEVATED, AND FEATURE A MODERATE
RISK (30-70% CHANCE) OF EXCEEDING 6 INCHES BOTH DAYS ACROSS THE
SOUTHERN SHORE OF LAKE SUPERIOR IN THE U.P. OF MI, AS WELL AS
PORTIONS OF NW L.P. NEAR TRAVERSE CITY, AND ACROSS THE TUG HILL
PLATEAU EAST OF LAKE ONTARIO. SLIGHTLY LOWER PROBABILITIES EXIST
ALONG THE CHAUTAUQUA RIDGE. SNOW TOTALS OF 1-2 FEET ARE POSSIBLE IN
THESE AREAS AS WELL. THEN DURING D3 THE FLOW BECOMES MORE WESTERLY
FOCUSING THE HEAVIEST LES ACROSS THE CHAUTAUQUA RIDGE AND TUG HILL
PLATEAU WHERE WPC PROBABILITIES INDICATE A HIGH CHANCE (>70%) FOR
ADDITIONAL SNOWFALL OF 6+ INCHES.
WEISS
...EXTREME COLD KEY MESSAGES ARE IN EFFECT. PLEASE SEE CURRENT KEY
MESSAGES BELOW...
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_1.PNG
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