Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 132029
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 PM EST WED DEC 13 2017

VALID 00Z THU DEC 14 2017 - 00Z SUN DEC 17 2017


...GREAT LAKES TO CENTRAL APPALACHIANS/NY/PA/SOUTHERN NEW
ENGLAND...

A QUICK MOVING ALBERTA CLIPPER SYSTEM AND SHORTWAVE TRACKING
SOUTHEASTWARD ACROSS THE OHIO VALLEY ACROSS PA/NJ/OFF THE COAST OF
SRN NY/NEW ENGLAND IS EXPECTED TO PRODUCE A SWATH OF SNOW IN THE
TERRAIN OF SOUTHWEST PENNSYLVANIA.  WITH THE SYSTEM BECOMING MORE
SHEARED AS IT MOVES EAST...THE ORIGINAL PARENT SFC LOW DECAYS AND
REFORMS OFF THE NEW ENGLAND COAST AND MOVES RAPIDLY OFFSHORE...SO
LIGHT AMOUNTS ARE EXPECTED ACROSS THE REST OF PA/SRN TIER OF
NY/NORTHERN NJ TO LONG ISLAND AND COASTAL SOUTHERN NEW
ENGLAND/ADJACENT ISLANDS.  TRENDS HAVE BEEN FOR THE LOW TRACK TO
BE SLIGHTLY NORTH OF THE PRIOR RUNS... SO THE SNOW AXIS IS A BIT
NORTH OF LAST NIGHT`S FORECASTS. PERIODS OF LAKE EFFECT SNOW ARE
LIKELY IN THE WAKE OF THIS SYSTEM WITH COLD AIR ADVECTION ACROSS
LK ERIE INTO NORTHWEST PA/ADJACENT SOUTHWEST NY/NORTHEAST OH.

ON DAY 2 IN THE LAKES...A DEVELOPING MID LEVEL TROUGH AND SFC
TROUGH CROSS THE UPPER LAKES...WITH CROSS LAKE FLOW IN THE
VICINITY OF LK SUPERIOR AND NORTHERN LK MICHIGAN SETTING UP
ENHANCED LEE SHORE CONVERGENCE AND AREAS OF LK EFFECT SNOW.
HIGHER AMOUNTS SHOULD FOCUS NEAR THE TRADITIONALLY FAVORED
TRAVERSE BAY IN NORTHWEST LOWER MI.

ON DAY 3..THE MID LEVEL TROUGH AND SFC REFLECTION MOVE INTO THE
LOWER LAKES...WITH LOCALLY HEAVY SNOWS DEVELOPING DOWNSTREAM FROM
THE LONGER CROSS LAKE FETCHES DOWNSTREAM FROM LK ERIE IN NORTHWEST
PA/SOUTHWEST NY AND ALSO DOWNSTREAM FROM LK ONTARIO IN THE TUG
HILL AND ADJACENT WESTERN ADIRONDACKS. THE GFS IS SUGGESTING A
DECREASE IN COVERAGE/INTENSITY LATE SAT AS THE TROUGH PASSES AND
DRIER AIR ALOFT ADVECTS ACROSS THE LAKE AND ADJACENT NORTHERN NY.

...SOUTHERN WY/CO ROCKIES DAY 1...

A SHORTWAVE DISTURBANCE TRACKING SOUTHWARD FROM WY INTO CO IS
EXPECTED TO PRODUCE COUPLED 700 MB CONVERGENCE/300 MB DIVERGENCE
MAXIMA TO PRODUCE LIFT IN ADVANCE OF THE UPPER LEVEL TROUGH.
ENHANCED MOISTURE IN THE REGION OF OROGRAPHIC FORCING AND SYNOPTIC
SCALE LIFT WILL LIKELY RESULT IN SNOW SHOWERS IN THE RANGES OF
CENTRAL CO.  WITH QPF GENERALLY BETWEEN A TENTH TO A QUARTER OF AN
INCH, COMBINED WITH SNOW RATIOS IN THE UPPER TEENS, SNOWFALL
AMOUNTS ON THE ORDER OF 3 TO 5 INCHES ARE EXPECTED, WITH ISOLATED
HIGHER AMOUNTS POSSIBLE OVER FAVORED TERRAIN.  THE SNOW TAPERS AS
THE UPPER TROUGH DEPARTS AND DRIER AIR MOVES INTO THE REGION THU.

...PACIFIC NORTHWEST AND NORTHERN ROCKIES DAY 3...

AN UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC RESULTS IN A JET
MAXIMA COMING INTO VANCOUVER ISLAND BY FRI MORNING AND NORTHERN ID
BY 00Z SAT.  THE APPROACH AND ARRIVAL OF THE UPPER TROUGH LEADS TO
A PERIOD OF ASCENT AND RESULTANT SNOW IN THE WA CASCADES AND THEN
THEN THE NORTHERN ROCKIES AS A WELL DEFINED STRIPE OF UPPER
DIVERGENCE PERSISTS IN THE RIGHT ENTRANCE REGION OF THE UPPER
LEVEL JET.  WITH THE WAVE AMPLIFYING FRI NIGHT INTO SAT AS IT
CROSSES MT/ID AND THEN WY...A PERIOD OF SNOW IS EXPECTED IN THE
RANGES WHERE THE WAVE CROSSES...WITH SEVERAL INCHES EXPECTED
ACCORDING TO THE 06-12Z GFS AND 00Z-12Z ECMWF...ALONG WITH
MULTIPLE ENSEMBLE MEMBERS. THE CONTINUING STEADY EASTWARD MOVEMENT
OF THE UPPER TROUGH LIMITS THE HEAVY SNOW POTENTIAL ACROSS THE
REGION.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAYS
1-3.

PETERSEN


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