Quantitative Precipitation Forecast
Issued by NWS

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774
FOUS11 KWBC 180902
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
501 AM EDT SAT MAR 18 2017

VALID 12Z SAT MAR 18 2017 - 12Z TUE MAR 21 2017


...UPPER OH VALLEY/NORTHERN MID ATLANTIC/NORTHEAST...

A WELL-DEFINED MID-UPPER LEVEL SHORTWAVE WILL CONTINUE TO MOVE
ACROSS THE GREAT LAKES REGION SAT MORNING...WITH A MID-UPPER LEVEL
CENTER FORECAST TO CLOSE OFF OVER THE LOWER GREAT LAKES/UPPER OH
VALLEY REGION LATER IN THE DAY.  THIS IS EXPECTED TO SUPPORT SOME
RAIN CHANGING TO SNOW SHOWERS...PRODUCING SOME LIGHT
ACCUMULATIONS...ALONG THE WESTERN PA-EASTERN WV MOUNTAINS.

AS THE UPPER LOW CONTINUES TO SLIDE TO THE EAST-SOUTHEAST TOWARD
THE NORTHERN MID ATLANTIC COAST...A SURFACE LOW IS FORECAST TO
DEVELOP JUST OFF OF THE NJ/DELMARVA SHORES ALONG A BAROCLINIC
BAND.  THIS LOW IS EXPECTED TO TRACK TO THE EAST...WELL SOUTH OF
LONG ISLAND SAT NIGHT BEFORE TURNING TO THE NORTH TOWARD THE
CANADIAN MARITIMES ON SUN.  LOW TO MID LEVEL THETA-E ADVECTION AND
FRONTOGENESIS IS EXPECTED TO SUPPORT ORGANIZED PRECIPITATION NORTH
OF THE LOW CENTER...WITH SOME ACCUMULATING SNOWS PERHAPS BRUSHING
LONG ISLAND AND THE NEW ENGLAND COAST.  OVERALL THE TREND IN THE
00 UTC GUIDANCE WAS FOR A STRONGER RIDGE ACROSS NORTHERN NEW
ENGLAND...WITH A MORE SOUTHERLY LOW TRACK OUT TO SEA.  THIS TREND
DOES NOT FAVOR THE GFS...WHICH MAINTAINED HEAVIER QPF/SNOW ACROSS
LONG ISLAND AND SOUTHERN NEW ENGLAND.  WPC PREFERRED THE LIGHTER
AMOUNTS OF THE NAM/ECMWF.  WPC PROBABILISTIC GUIDANCE SHOWS ONLY A
SLIGHT RISK FOR SNOW ACCUMULATIONS OF 4-INCHES OR MORE FROM
NORTHEASTERN PA TO SOUTHEASTERN MA ON DAY 1 (ENDING 12 UTC SUN)
AND THEN FROM EASTERN MA TO ALONG MUCH OF THE MAINE COAST ON DAY 2
(ENDING 12 UTC MON).  WITH THE LOW EXPECTED TO TURN TO THE NORTH
ON SUN...PROBABILITIES ARE HIGHER ACROSS DOWNEAST MAINE...WITH A
MODERATE RISK FOR 4-INCHES AND A SLIGHT RISK FOR 8-INCHES OR MORE
DURING THE DAY 2 PERIOD.

THE PROBABILITY OF ICE ACCUMULATIONS OF 0.25 INCH OR MORE IS LESS
THAN 10 PERCENT.

...WESTERN U.S....

A MID-UPPER LEVEL TROUGH AND ITS ASSOCIATED COLD FRONT ARE
EXPECTED TO MOVE INLAND...BRINGING SNOW LEVELS DOWN ACROSS THE
NORTHWEST ON SAT...WITH HEAVY ACCUMULATIONS POSSIBLE ACROSS THE
NORTHERN CASCADES.  THE TROUGH IS EXPECTED TO MOVE STEADILY EAST
INTO CENTRAL CANADA BY EARLY SUN.  ITS TRAILING COLD FRONT IS
EXPECTED TO SETTLE INTO AND THEN LINGER ACROSS NORTHERN WY INTO
EARLY TUE...WHERE IT WILL PROVIDE A FOCUS FOR SNOW SHOWERS AND
PERHAPS SOME LOCALLY HEAVY ACCUMULATIONS ALONG THE NORTHWESTERN
WY/SOUTHWESTERN MT RANGES.

THE PROBABILITY OF ICE ACCUMULATIONS OF 0.25 INCH OR MORE IS LESS
THAN 10 PERCENT.

PEREIRA

$$





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