824
FOUS11 KWBC 120908
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 AM EST FRI DEC 12 2025
VALID 12Z FRI DEC 12 2025 - 12Z MON DEC 15 2025
..MONTANA
DAY 1...
NWLY JET DOWNSTREAM OF AN AMPLIFYING RIDGE AXIS OFF THE PACNW COAST
CONTINUES TO INTENSIFY THROUGH THIS MORNING WITH 250MB WINDS
INCREASING ABOVE 150KT OVER SOUTH-CENTRAL ALBERTA. PACIFIC MOISTURE
CONTINUES TO SHIFT INLAND SOUTH OF THIS JET WHICH MEETS
PARTICULARLY COLD AIR FROM THE CANADIAN PRAIRIES THAT IS BANKING
UP AGAINST THE EASTERN SLOPES OF THE MT ROCKIES. THE AMPLIFYING
RIDGE MAINTAINS THE JET DYNAMICS WITH BANDING OVER CENTRAL MT NOW
EXPECTED TO DRIFT NORTH TO NORTHERN MT THROUGH THIS EVENING BEFORE
EJECTING SOUTHEAST OVER THE NORTH-CENTRAL PLAINS LATE
TONIGHT/SATURDAY MORNING.
ONGOING FREEZING RAIN ALONG THE SOUTHERN PERIPHERY OF THE BANDING
IN VALLEYS IN THE EASTERN SLOPES WILL CONTINUE THIS MORNING WITH
ONLY A NARROW STRIP OF WINTRY MIX SHIFTING NORTH WITH THE SOUTHERN
EXTENSION REST OF TODAY. OTHERWISE THIS IS FLUFFY WITH CONSISTENT
0.5"/HR RATES ACROSS THE MT PLAINS THROUGH THIS EVENING (PER 00Z
HREF) WITH SLR IN THE 15 TO 18:1 RANGE. DAY 1 PWPF FOR >6" SNOW IS
OVER 40% ACROSS MUCH OF NORTH-CENTRAL TO EASTERN MT, INCLUDING
AROUND HAVRE WHERE PROBABILITIES ARE ABOVE 70%.
...NORTHERN PLAINS THROUGH THE MIDWEST TO THE CENTRAL
APPALACHIANS... DAYS 1-2...
A REINFORCING TROUGH OVER THE GULF OF ALASKA EARLY THIS MORNING
RIDES AN INCREASING NWLY JET TODAY, REACHING SOUTHERN SASKATCHEWAN
TONIGHT. THIS TROUGH IS THE CATALYST FOR ALLOWING ONGOING SNOW
BANDING OVER MT TO EJECT SOUTHEAST ACROSS THE DAKOTAS LATE TONIGHT
AND THE MIDWEST SATURDAY. STRONG JET DYNAMICS AND AMPLE COLD AIR
WITH ARCTIC ORIGIN ALLOWS FOR DECENT SNOW RATES THROUGH THIS SWATH,
CONSISTENTLY OVER 0.5"/HR PER THE 00Z HREF. DAY 1.5 PWPF FOR >4"
ARE LOWER OVER SOUTH DAKOTA WHERE THE BANDS ARE FAIRLY PROGRESSIVE,
GENERALLY 30%, BUT HIGHER OVER IOWA THROUGH NORTH-CENTRAL IL AND
CENTRAL IN WHERE THE BAND PIVOTS EAST WITH VALUES OF 40-60%.
PROBABILITIES CONTINUE TO RAMP UP TO THE EAST OVER OHIO LATER
SATURDAY BEFORE OROGRAPHIC LIFT BRINGS INCREASING PROBABILITIES
FOR >6" TO NORTHERN WV, PEAKING FOR AREAS JUST WEST OF THE
ALLEGHENY FRONT WHERE DAY 2 PWPF FOR >6" ARE 40-70%.
THIS SWATH IS FORECAST TO BE A BIT NORTH OF THE CURRENT SNOW
TRACKING EAST FROM SOUTHERN IN AND EASTERN KY. THESE TWO
CLIPPERS WILL PRODUCE DECENT SWATHS OF SNOW AND COMBINE TO COVER
LARGE AREAS OF THE MIDWEST WITH SNOW THROUGH SATURDAY.
..MID-ATLANTIC THROUGH THE COASTAL NORTHEAST
DAYS 2-3...
THE SATURDAY SHORTWAVE TROUGH/CLIPPER AMPLIFIES AN UPPER LOW OVER
LAKE SUPERIOR SATURDAY ALLOWING IT TO FURTHER DEVELOP AND DIG
SOUTH OVER THE EASTERN GREAT LAKES SATURDAY NIGHT. THE SURFACE
COMPONENT OF THIS LOW DEVELOPS AS A TROUGH OFF THE MID-ATLANTIC
COAST TO THE OUTER BANKS BY 12Z SUNDAY. RIGHT ENTRANCE JET DYNAMICS
AND THIS DEVELOPING SURFACE TROUGH ALLOW MODERATE TO LOCALLY HEAVY
BANDING TO DEVELOP OVER THE CENTRAL/NORTHERN MID-ATLANTIC THROUGH
SOUTHERN NEW ENGLAND SATURDAY NIGHT INTO SUNDAY. PLACEMENT OF
BANDING WITH A KEY AREA OF 0.25" QPF REMAINS A BIT UNCERTAIN AT
THIS TIME, BUT AREAS FROM BALTIMORE THROUGH NEW JERSEY AND
POSSIBLE LONG ISLAND ARE OF MOST CONCERN NOW. DAY 2.5 PWPF FOR >4"
ARE 30-40% AROUND PHILLY AND AROUND 20% OVER SOUTHERN CONNECTICUT
THROUGH SOUTHEAST MASS. CONFIDENCE HAS INCREASED ON THE SNOW
ADVANCING AND REACHING THE NYC METRO LATE SATURDAY EVENING.
RAPID LOW PRESSURE DEVELOPMENT IS EXPECTED OFF THE NORTHEAST COAST
SUNDAY WHICH WILL MAINTAIN OFFSHORE FLOW AND SHOULD ALLOW OCEAN/BAY
ENHANCED SNOW FOR THE CAPE AND ISLANDS THROUGH SUNDAY NIGHT. DAY 3
PWPF FOR >4" ARE AROUND 30% FOR CAPE COD.
..GREAT LAKES
DAYS 1-3...
PERSISTENT TROUGHING ACROSS THE EAST WILL MAINTAIN COLD CONDITIONS
AS A STORM BRINGS ANOTHER ROUND OF LAKE ENHANCED AND EFFECT SNOW
ACROSS THE GREAT LAKES TONIGHT THROUGH SUNDAY. LOW PRESSURE
CURRENTLY OVER MANITOBA DIVES SOUTHEAST TO LAKE SUPERIOR TONIGHT
BEFORE AMPLIFYING BY AN AFOREMENTIONED SHORTWAVE TROUGH. WESTERLY
FLOW AHEAD OF THIS LOW BRINGS SYNOPTIC SNOW WITH LAKE ENHANCEMENTS
FOR THE U.P. AND TIP OF THE L.P. MITT WHERE DAY 1.5 PWPF FOR >6"
ARE 30-50%.
THIS WESTERLY FLOW THEN CROSSES THE EASTERN GREAT LAKES EARLY
SATURDAY BRINGING RENEWED COLD AIR ADVECTION AND TRANSIENT SINGLE-
BANDING TO SNOW BELTS EAST OF CLEVELAND THROUGH THE CHAUTAUQUA
RIDGE AND ACROSS THE TUG HILL WHERE DAY 2 PWPF FOR >6" ARE 40-70%.
LES THEN CONTINUES ON NWLY FLOW BEHIND THE LOW ON SUNDAY WITH DAY 3
PWPF FOR >4" 40-80% IN NORTHWEST PA AND AROUND SYRACUSE.
JACKSON
..EXTREME COLD KEY MESSAGES ARE IN EFFECT AND LINKED BELOW
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_1.PNG
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