359
FOUS11 KWBC 132003
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM EST SAT DEC 13 2025
VALID 00Z SUN DEC 14 2025 - 00Z WED DEC 17 2025
..UPPER OHIO VALLEY TO CENTRAL APPALACHIANS
DAYS 1-2...
MODERATE TO HEAVY SNOW WILL BE ONGOING AT THE START OF THE FORECAST
PERIOD (00Z SUN) ACROSS THE OHIO VALLEY INTO THE CENTRAL
APPALACHIANS WITH UPSLOPE SNOW CONTINUING ALONG THE HIGHER TERRAIN
THROUGH MONDAY MORNING. A MID- LEVEL LOW ASSOCIATED WITH THIS
SNOWFALL IS OVER NORTHEAST SHORE OF LAKE SUPERIOR WITH A
REINFORCING SHORTWAVE TROUGH OVER THE UPPER MIDWEST. THIS WAVE IS
RIDING A POWERFUL 140KT JET THAT EXTENDS ACROSS THE MIDWEST AND
THROUGH THE MID- ATLANTIC. INTENSIFYING 700 MB FGEN (BOTH THROUGH
WAA AND THE RESULT OF THE UPPER JET STREAK POSITION) WILL BE
SUFFICIENT TO DRIVE OMEGA THROUGH A WIDE (GREATER THAN 100 MB) SNOW
GROWTH ZONE THROUGH THIS EVENING. WITH STRONG LIFT OCCURRING INTO
A DGZ THAT IS DEEPENING IN THE COLD AIRMASS, PERIODS OF HEAVY SNOW
AND HIGH SNOW RATIOS (AROUND 20:1) ARE EXPECTED, ESPECIALLY WITHIN
A NARROW TRANSLATING BAND FROM OHIO INTO NORTHERN WV TODAY,
SOUTHWEST PA AND FAR WESTERN MD TONIGHT.
THE BANDS RISE OVER THE ALLEGHENY PLATEAU THIS EVENING WHERE
OROGRAPHY BRINGS A RISK FOR 1"/HR RATES. FOLLOWING THIS SYSTEM A
STRONG ARCTIC COLD FRONT PUSHES SOUTHWARD AND PROMOTES LAKE
ENHANCED UPSLOPE FLOW INTO THE HIGH ELEVATIONS OF SOUTHWEST PA,
WESTERN MD, AND WV. DAY 1 PWPF FOR >6" ARE AROUND 40% TO 70% ACROSS
NORTH- CENTRAL WV INTO WESTERN MD AND SOUTHWEST PA.
..MID-ATLANTIC THROUGH SOUTHERN NEW ENGLAND
DAY 1...
THE SAME SYSTEM IMPACTING THE OHIO VALLEY SHIFTS TOWARDS THE MID-
ATLANTIC AND NORTHEAST TONIGHT AS THE UPPER LOW STALLS OVER
NORTHERN LAKE SUPERIOR BEFORE EJECTING SOUTHEAST WITH THE AID OF A
REINFORCING SHORTWAVE. THE RESULTANT UPPER TROUGH AXIS REACHES THE
NORTHEASTERN SEABOARD SUNDAY EVENING WITH DOWNSTREAM SURFACE
TROUGH THEN LOW DEVELOPMENT OFF THE MID- ATLANTIC COAST SUNDAY
MORNING. STRONG RIGHT ENTRANCE DYNAMICS AID FGEN BANDING TO
DEVELOP IN THE LEE OF THE CENTRAL APPS LATER THIS EVENING, MOST
LIKELY OVER NORTH-CENTRAL MD EAST THROUGH NJ BEFORE THE SURFACE
TROUGH/LOW OFFSHORE PROVIDES ADDITIONAL FORCING FOR MORE INTENSE
BANDING OVERNIGHT AND SHIFTS THE BAND SOUTH AND EAST. THIS SYSTEM
IS FAIRLY PROGRESSIVE, BUT THE FRONTAL FORCING IN INCREASINGLY COLD
AIR ALLOWS 0.5-1.0"/HR RATES IN THE MID- ATLANTIC, EXTENDING TO FAR
SOUTHERN NEW ENGLAND EARLY SUNDAY. MARGINAL THERMALS AT THE
SOUTHERN EXTEND OF THE PRECIP SWATH TO BEGIN WITH QUICKLY SHIFT TO
ALL SNOW - THIS IS AIDED BY THE NIGHTTIME OCCURRENCE. SNOW RATIOS
COULD TIP THE SCALES TO HIGHER END AMOUNTS ACROSS PARTS OF EASTERN
PA THROUGH LONG ISLAND AND SOUTHERN NEW ENGLAND AS OMEGA INTERSECTS
WITH A WIDE DGZ AS THE PRECIPITATION SHIELD PULLS EASTWARD,
SUPPORTING RATIOS CLOSER TO 15-20:1 AND MUCH HIGHER THAN
CLIMATOLOGY.
THIS EVENT SHOULD LAST NO MORE THAN 6-12 HOURS IN ANY GIVEN
LOCATION, AND THE EXACT PLACEMENT, TIMING, AND INTENSITY OF THE JET
STREAK AND OFFSHORE TROUGH IS STILL SOMEWHAT UNCERTAIN. TODAY'S
GUIDANCE TRENDED A TICK NORTH AND WETTER DUE TO A MORE AMPLIFIED
UPPER TROUGH AND RELATED RIGHT ENTRANCE REGION OF A 150KT UPPER
JET. DAY 1 PWPF FOR >6" ARE 30-50% FROM NORTH-CENTRAL MD THROUGH
SOUTHEAST PA AND CENTRAL NJ. PROBABILITIES FOR >6" ARE 20-40%
ACROSS LONG ISLAND AND CAPE COD, INCLUDING THE ISLANDS OFF SOUTHERN
NEW ENGLAND. GIVEN MOST OF THIS SNOW IS EXPECTED TO OCCUR
OVERNIGHT AND DURING A WEEKEND, IMPACTS MAY BE LIMITED, BUT STRONG
COLD AIR ADVECTION FOLLOWING THE EVENT AND VERY COLD TEMPERATURES
COULD POSE A DANGER FOR INDIVIDUALS CAUGHT UNPREPARED OUTDOORS. BE
SURE TO CHECK CONDITIONS BEFORE TRAVELING IN THIS REGION TONIGHT OR
TOMORROW MORNING.
..GREAT LAKES
DAYS 1-3...
AFOREMENTIONED LOW PRESSURE SYSTEM STALLING OVER LAKE SUPERIOR
TODAY EJECTS SOUTHEAST TONIGHT WITH A REINFORCING SHORTWAVE TROUGH
PASSAGE ON MONDAY. SUBTERRANEAN DGZ UNDER THE LOW TODAY MAKES FOR
COARSE/LOW SLR SNOW, BUT SOME WARMING THIS EVENING BRINGS BACK THE
DENDRITES AND 20:1 SLRS TO THE U.P.
DAY 1 PWPF FOR >6" ARE 40-80% OVER NWLY FLOW SNOW BELTS IN THE
EASTERN U.P. AND EAST OF GRAND TRAVERSE BAY. WLY FLOW SNOW BELTS
EAST OF LAKES ERIE/ONTARIO RESULT IN DAY 1 PWPF >6" OF 30-50% EAST
OF CLEVELAND TO THE CHAUTAUQUA RIDGE AND OVER 80% FOR THE TUG HILL
WHERE SINGLE BANDING LES SETS UP THIS EVENING. LULL EXPECTED
FOR SUNDAY NIGHT AS LOW LEVEL RIDGING SHIFTS EAST OF THE LAKES. BUT
THEN SHORTWAVE CROSSES MONDAY WITH A DECENT, BUT TRANSIENT SWATH OF
LAKE ENHANCED SNOW. LIGHT TO LOCALLY MODERATE SYNOPTICALLY DRIVEN
SNOW ACROSS THE GREAT LAKES REGION MONDAY WITH MORE SINGLE BANDING
IN WESTERLY FLOW OVER LAKE ONTARIO INTO THE TUG HILL WHERE DAY 2.5
PWPF FOR >8" IS OVER 80%.
..PACIFIC NORTHWEST
DAYS 2-3...
POTENT ATMOSPHERIC RIVER ARRIVES MONDAY MORNING TO WESTERN WA/OR
WITH SNOW LEVELS SKYROCKETING UP TO 9000FT OVER THE CASCADES. A
SHORTWAVE TROUGH PASSAGE OVER WA LATE MONDAY BRINGS SNOW LEVELS ON
THE NORTH CASCADES DOWN TO 5000FT, REACHING 4000FT ON TUESDAY.
LOWER PRECIP RATES ARE EXPECTED BEHIND THE TROUGH PASSAGE, BUT
MODERATE SNOW BRINGS DAYS 2-3 PWPF FOR >8" IN THE 60-90% RANGE IN
THE HIGH NORTHERN WA CASCADES. ADDITIONAL SNOW IS EXPECTED FOR
THIS REGION AFTER THE SHORT RANGE FORECAST PERIOD ENDS BY 00Z
WEDNESDAY.
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
SNELL/JACKSON
...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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