934
FOUS11 KWBC 112224
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
524 PM EST THU DEC 11 2025
VALID 00Z FRI DEC 12 2025 - 00Z MON DEC 15 2025
..MONTANA
DAYS 1-2...
A SECOND ROUND OF HEAVY SNOWFALL (ALTHOUGH WITH MINIMAL BREAK FROM
THE FIRST) WILL DEVELOP ACROSS MT, GENERALLY EAST OF THE
CONTINENTAL DIVIDE AND EXPAND INTO THE HIGH PLAINS. THIS WILL BE
THE RESULT OF OVERLAPPING ASCENT SLOWLY SHIFTING NORTHEAST WITH
TIME INTO A COLD AND ANOMALOUSLY MOIST ENVIRONMENT.
THE EVENT BEGINS TO EXPAND AS A POWERFUL (150+ KT) PACIFIC JET
STREAK BEGINS TO PIVOT NORTHEAST, WHILE A STRONG COLD FRONT
CONTINUES TO WAVER NW TO SE AND BANK INTO THE TERRAIN. THE OVERLAP
OF THIS JET AND ITS ACCOMPANYING IVT (STILL > 90% PROBABILITY OF
EXCEEDING 250 KG/M/S SPILLING EAST OF THE TERRAIN) WILL HELP EXPAND
PRECIPITATION ONCE AGAIN ACROSS THE AREA. THIS WILL FALL
EXCLUSIVELY AS SNOW THANKS TO RAPID COLUMN COOLING BEHIND THE
FRONT. THE ACCOMPANYING WESTERLY FLOW ALOFT, WHILE NOT IDEAL FOR
COLUMN MOISTENING, WILL LEAD TO AT LEAST MODEST ISENTROPIC ASCENT
ATOP THE COLD FRONT, PRIMARILY ALONG THE 290K-295K SURFACES,
HELPING TO EXPAND THE SNOW SWATH. AT THE SAME TIME, PERSISTENT
700-600MB FGEN WILL DRIFT ACROSS THE AREA, AIDED BY THE ENTRANCE
REGION TO THE UPPER JET, AND DRIVING ASCENT EFFICIENTLY INTO THE
DEEPENING DGZ (30% PROBABILITY FROM THE SREF FOR DGZ DEPTH
EXCEEDING 100MB) SUGGEST THE POTENTIAL FOR PERIODS OF HEAVY
SNOWFALL RATES EXCEEDING 1"/HR (UP TO 70% CHANCE FRIDAY EVENING).
TEMPERATURES WILL BE QUITE COLD, SO SLRS ARE EXPECTED TO BE FLUFFY
AND ABOVE-CLIMO WHICH SHOULD RESULT IN RAPID ACCUMULATION OF
SNOWFALL. THIS WILL BE MOST PRONOUNCED WHERE ANY JET-ENHANCED
BANDING CAN OCCUR, ESPECIALLY DUE TO THE PROLONGED AND NEARLY-
STATIONARY NATURE OF THE UPPER JET ALOFT. THIS IS REFLECTED BY WPC
PROBABILITIES THAT SUPPORT A MODERATE RISK (50-90%) FOR AT LEAST 6
INCHES OF SNOW ACROSS CENTRAL MT JUST EAST OF THE TERRAIN, WITH
LOCALLY AS MUCH AS 12" POSSIBLE (10-30%), AND LOCALLY HIGHER
AMOUNTS IN THE MOUNTAINS.
..GREAT LAKES INTO NORTHEAST
DAYS 1-3...
PERSISTENT TROUGHING ACROSS THE EAST WILL KEEP CYCLONIC FLOW IN
PLACE ACROSS THE GREAT LAKES AND INTO THE NORTHEAST THROUGH THE
WEEKEND, WHILE PERIODIC SHORTWAVE IMPULSES ROTATE SOUTHEAST THROUGH
THE FLOW. EACH OF THESE SHORTWAVES WILL RESULT IN TRANSIENT
ENHANCED ASCENT, WITH THE MOST IMPRESSIVE HEIGHT FALLS LIKELY D3 AS
THE LAST IN THIS SERIES OF SHORTWAVES AMPLIFIES SHARPLY LATE IN THE
FORECAST PERIOD.
THE RESULT OF THIS EVOLUTION WILL BE PERIODS OF LIGHT SYNOPTIC SNOW
ASSOCIATED WITH EACH SHORTWAVE, FOLLOWED BY MORE IMPRESSIVE LAKE
EFFECT SNOW (LES) OR LAKE-ENHANCED SNOW. WHILE MANY AREAS WILL
LIKELY EXPERIENCE AT LEAST LIGHT SYNOPTIC SNOW, ANY SIGNIFICANT
ACCUMULATIONS ARE EXPECTED TO BE CONFINED TO LAKE EFFECT SNOW AREAS
ON THE PERSISTENT W/NW FLOW, WITH ENHANCEMENT OCCURRING BEHIND
EACH SHORTWAVE AND THE ACCOMPANYING CAA. ON D1, MODEST LES, WHICH
HAS A WPC PROBABILITY OF 10-30% FOR EXCEEDING 4" IS CONFINED TO THE
KEWEENAW PENINSULA OF MI AND JUST EAST OF LAKE ONTARIO.
HOWEVER, DURING D2 AND D3, LES BECOMES MORE WIDESPREAD AND
INTENSE. WITH 850MB TEMPS CRASHING TO POTENTIALLY LESS THAN -20C
OVER THE LAKE TEMPERATURES THAT ARE STILL GENERALLY +2C TO +8C WILL
CREATE DEEP INVERSION DEPTHS AND IMPRESSIVE LAKE-INDUCED
INSTABILITY TO SUPPORT HEAVY LES. SNOWFALL RATES OF AT LEAST 2"/HR
APPEAR PROBABLE, ESPECIALLY ACROSS THE U.P. AND THEN EAST OF LAKES
ERIE/ONTARIO WHERE UPSTREAM CONNECTION MAY ADDITIONALLY OCCUR. WPC
PROBABILITIES D2 FOR 4+ INCHES OF SNOW ARE ABOVE 50% ACROSS MUCH OF
THE SOUTHERN SHORE OF LAKE SUPERIOR IN THE U.P., AS WELL AS NEAR
BUFFALO, NY AND INTO THE TUG HILL PLATEAU. BY D3, THESE
PROBABILITIES EXPAND TO INCLUDE THE NW AND SW L.P. OF MI AS WELL AS
THE BREADTH OF THE CHAUTAUQUA RIDGE. 2-DAY SNOWFALL TOTALS FROM THE
LES (D2-D3) COULD 18" IN SOME AREAS.
..NORTHERN PLAINS THROUGH THE OHIO VALLEY
DAYS 1-3...
PINCHED CYCLONIC FLOW ON THE PERIPHERY OF AN AMPLIFYING TROUGH OVER
SOUTHEAST CANADA WILL KEEP FLOW PROGRESSIVE FROM THE NORTHERN
PLAINS THROUGH THE OHIO VALLEY, WHILE DUAL POTENT SHORTWAVE TROUGHS
ROTATE THROUGH THE FLOW.
THE FIRST OF THESE WILL BE ACCOMPANIED BY A STRUNG OUT LOBE OF
VORTICITY RACING FROM SOUTH DAKOTA EARLY D1 TO THE MID-ATLANTIC
COAST EARLY D2. THE SPEED OF THIS SYSTEM WILL SOMEWHAT LIMIT THE
POTENTIAL FOR HEAVY PRECIPITATION. HOWEVER, FORCING FOR ASCENT WILL
MAXIMIZE ON THE PERIPHERY OF A POTENT UPPER JET STREAK DIGGING
SOUTHEAST COINCIDENT WITH A NARROW CORRIDOR OF IMPRESSIVE 290K
ISENTROPIC ASCENT AND 925-700MB FGEN. THE MOST INTENSE ASCENT IS
EXPECTED FROM IOWA INTO KENTUCKY WHERE A BAND OF HEAVY SNOWFALL IS
LIKELY TO TRANSLATE SOUTHEAST ON THE EDGE OF THE STRONGEST WAA.
THIS WILL CREATE A STRIPE OF MODERATE SNOWFALL WITH BRIEFLY HEAVY
SNOW RATES EXCEEDING 1"/HR POSSIBLE (30% CHANCE). WPC PROBABILITIES
FOR THIS LEAD SHORTWAVE REACH 30-50% FOR 4+ INCHES, WITH LOCALLY
6+" POSSIBLE (10-30%) IN IL/IN.
IMMEDIATELY FOLLOWING THIS FIRST WAVE WILL BE A SECOND SHORTWAVE
WITH MORE IMPRESSIVE AMPLITUDE, LEADING TO A SECOND STREAK OF
MODERATE TO HEAVY SNOWFALL CROSSING ALMOST THE IDENTICAL PATH.
ALTHOUGH THERE IS CONSIDERABLE LATITUDINAL SPREAD AMONG THE
GUIDANCE, IT IS PROBABLE THAT THE LEAD SHORTWAVE WILL PUSH THE
BAROCLINIC GRADIENT SOUTH TO SUPPORT A SLIGHT SOUTHWARD PUSH OF
HEAVY SNOW WITH THE NEXT WAVE, AT LEAST UNTIL AMPLIFICATION OF THE
MID-LEVEL PATTERN OCCURS SATURDAY EVENING WHICH COULD RESULT IN THE
HEAVIEST AXIS AGAIN MOVING ACROSS CENTRAL IN AND THEN INTO THE
LOWER OHIO VALLEY. ANOTHER STRIPE OF MODERATE TO HEAVY SNOW IS
LIKELY DESPITE THE TRANSIENT NATURE OF THE EVENT AS THE DGZ REMAINS
ELEVATED AND 700-600MB FGEN INCREASES WHICH CROSSES DIRECTLY INTO
THE DGZ TO PRODUCE AMPLE SNOW GROWTH POTENTIAL. REGIONAL SOUNDINGS
ACROSS THIS AREA ALSO INDICATE A NEAR-ISOTHERMAL LAYER BENEATH THE
DGZ, AND WHILE TEMPERATURES ARE COLD, SHOULD STILL SUPPORT FLUFFY
SLR WITH EFFICIENT ACCUMULATIONS. AT THIS TIME, WPC PROBABILITIES
ON D2 INDICATE A 30-50% CHANCE OF AN ADDITIONAL 4+ INCHES IN
CENTRAL IL, REACHING 30-70% D3 FROM IN THROUGH SOUTHERN OH.
ALTHOUGH THERE WILL BE A BREAK BETWEEN THESE TWO EVENTS, SOME AREAS
COULD RECEIVE DOUBLE-DIGIT SNOWFALL BY THE TIME BOTH OF THESE
EVENTS ARE OVER, AND WITH COLD TEMPERATURES IN PLACE, THIS WILL
LIKELY CREATE HAZARDOUS TRAVEL FOR THE REGION.
..CENTRAL APPALACHIANS AND MID-ATLANTIC
DAYS 1-3...
THE SAME IMPULSES/CLIPPERS BRINGING SNOW TO THE PLAINS/MIDWEST WILL
TRACK E/SE INTO THE CENTRAL APPALACHIANS AND MID-ATLANTIC STATES.
THE FIRST OF THESE WILL BE EXITING THE COAST FRIDAY MORNING, AND
WHILE SNOW WILL GENERALLY BE MODEST, THE ADDITION OF UPSLOPE FLOW
ON W/NW WINDS INTO THE CENTRAL APPALACHIANS WILL RESULT IN MODERATE
ACCUMULATIONS ACROSS THE TERRAIN OF WV. HERE, WPC PROBABILITIES D1
INTO D2 SUPPORT A LOW RISK (10-30+%) OF AT LEAST 4 INCHES OF
SNOWFALL.
THE MORE SIGNIFICANT EVENT IS WITH THE SECONDARY IMPULSE WHICH WILL
BE INTENSIFYING D3 AS THE MID-LEVEL PATTERN AMPLIFIES AND SWINGS
THE PRIMARY TROUGH AXIS INTO THE CENTRAL APPALACHIANS AND MID-
ATLANTIC SUNDAY MORNING. THIS WILL DRIVE RAPID HEIGHT FALLS INTO
THE AREA, WHILE THE SHARPENING TROUGH AXIS WILL HELP ARC THE
DOWNSTREAM JET STREAK POLEWARD TO PRODUCE RAPIDLY INTENSIFYING
UPPER DIFFLUENCE WITHIN THE RRQ. WESTERLY MID-LEVEL FLOW WILL CAUSE
IMPRESSIVE UPSLOPE FLOW INTO THE TERRAIN OF WV/MD/PA ONCE AGAIN,
BUT IN THIS CAUSE THE AVAILABLE MOISTURE WILL BE MORE SIGNIFICANT,
WHICH WHEN ADDED TO THE ROBUST DEEP LAYER ASCENT RESULTS IN WPC
PROBABILITIES THAT EXCEED 50% FOR 6+ INCHES FROM THE LAUREL
HIGHLANDS THROUGH CENTRAL WV, WITH LOCALLY MORE THAN 10 INCHES
POSSIBLE.
THE MORE CHALLENGING ASPECT OF THIS FORECAST IS WHAT HAPPENS ACROSS
THE COASTAL MID-ATLANTIC STATES, INCLUDING THE I-95 CORRIDOR. AS
THE UPPER JET INTENSIFIES AND ARCS, IT WILL LIKELY PROVIDE ENOUGH
ASCENT DOWNSTREAM OF THE SHARPENING TROUGH TO PRODUCE A SECONDARY
AXIS OF MODERATE TO HEAVY SNOW IN THE VICINITY OF I-95. THE SPEED
AT WHICH THIS TROUGH DEEPENS AND THE CORRESPONDING JET AMPLIFIES
WILL DRIVE THE POSITION OF THE HEAVY SNOW AXIS, WHICH REMAINS QUITE
UNCERTAIN AT THIS TIME. HOWEVER, WITH THE PV ANOMALY SWINGING EAST
AND POTENTIALLY PUSHING THE 1.5 PVU SURFACE DOWN BELOW 450MB, THIS
COULD BE A BRIEFLY INTENSE EVENT DOWNSTREAM.
EVALUATION OF THE RECENT CLUSTER ANALYSIS INDICATES THAT THE
PRIMARY EOF /UNCERTAINTY/ REVOLVES AROUND THE SPEED OF THIS TROUGH
AMPLIFICATION, AND THERE IS QUITE A BIT OF SPREAD AMONG THE VARIOUS
CLUSTERS. IN GENERAL, THE EC MEMBERS ARE BIT SLOWER AND DEEPER,
WHILE THE GEFS MEMBERS ARE A LITTLE FASTER AND WEAKER. SOMEWHERE IN
THE MIDDLE IS PROBABLY REASONABLE AT THIS TIME, WHICH RESULTS IN A
STRIPE OF HEAVY SNOW THAT WILL DEVELOP WITHIN INCREASING 850-700MB
FGEN SOMEWHERE NEAR I-95 FROM WASHINGTON, D.C. THROUGH NYC AND
INTO CAPE COD, MA. THERE IS STILL A LOT OF SPREAD, BUT WHERE THIS
BAND DEVELOPS, WHICH IS CURRENTLY EXPECTED NEAR I-95, WPC
PROBABILITIES ARE MODERATE (50-70%) FOR AT LEAST 2 INCHES OF SNOW
BETWEEN DC AND NYC, WITH LOCALLY MORE THAN 4 INCHES POSSIBLE.
CONSIDERABLE ADJUSTMENTS TO THE LOCATION OF THIS BAND ARE STILL
POSSIBLE, SO FURTHER REFINEMENTS TO THE LOCATION AND ACCOMPANYING
PROBABILITIES CAN BE EXPECTED IN THE NEXT FEW FORECAST CYCLES.
WEISS
...EXTREME COLD 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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