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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0749Z Mar 31, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
349 AM EDT TUE MAR 31 2015

VALID 12Z TUE MAR 31 2015 - 12Z FRI APR 03 2015


DAYS 1-3...

...NORTHERN MID-ATLANTIC ON TUE...

A NARROW SWATH OF SNOW ACCUMULATIONS OF 4-INCHES OR
MORE...ASSOCIATED WITH A CLIPPER SYSTEM DIVING OUT OF THE GREAT
LAKES...IS POSSIBLE LATER TODAY ACROSS PORTIONS OF NORTHERN
PA...NORTHWESTERN NJ AND THE CATSKILL MOUNTAIN REGION OF NY. THE
GREATEST POTENTIAL IS EXPECTED TO CENTER ACROSS THE ALLEGHENY
PLATEAU/MOUNTAINS IN NORTHWESTERN PA.  WPC PREFERRED A BLEND OF
THE ECMWF/NAM WITH RESPECT TO THE TIMING OF THE SYSTEM...ALTHOUGH
SUSPECT THE MORE NORTHERLY AXIS OF THE NAM IS A REFLECTION OF ITS
TYPICAL BIAS.  ALSO SUSPECT ITS AMOUNTS ARE TOO HEAVY...ANOTHER
BIAS THE MODELS HAVE SHOWN WITH SIMILAR SYSTEMS AS OF LATE.  AS
NOTED IN THE PMDHMD...THE GFS BECOMES A RELATIVELY FAST OUTLIER
WITH THIS SYSTEM DURING THE PERIOD...AND IT TOO MAY BE OVERDONE
WITH ITS QPF.  GIVEN THE SUSPECTED WET BIAS OF THE MODELS AND HIGH
SUN ANGLE THIS SYSTEM WILL HAVE TO CONTEND WITH...OPTED FOR
AMOUNTS A LITTLE MORE CONSERVATIVE THAT WHAT THE NCEP GUIDANCE
OFFERED. 

...PACIFIC NORTHWEST TO THE NORTHERN ROCKIES ON TUE-WED...

SIGNIFICANT HEIGHT FALLS ASSOCIATED WITH A WELL-DEFINED SHORTWAVE
ARE EXPECTED TO CONTINUE EAST ACROSS THE NORTHWEST TODAY.  THE
STRONG MID-UPPER LEVEL DYNAMICS ASSOCIATED WITH THE
TROUGH...FOLLOWED BY PERSISTENT ONSHORE FLOW IN THE WAKE OF THE
ASSOCIATED SURFACE FRONT IS EXPECTED TO PRODUCE LOCALLY HEAVY
PRECIPITATION ACROSS THE NORTHERN CASCADES...WHERE SEVERAL INCHES
OF SNOW CAN BE EXPECTED...BEFORE RIDGING AND DRIER CONDITIONS
RETURN TO THE REGION BY EARLY THU.  WPC AMOUNTS FAVORED A BLEND OF
THE GFS/ECMWF.

...CENTRAL ROCKIES/HIGH PLAINS...

THE SHORTWAVE MOVING INTO THE NORTHWEST ON TUE IS EXPECTED TO
CONTINUE ACROSS THE NORTHERN TIER U.S....REACHING THE GREAT LAKES
THU NIGHT.  A STRONG ASSOCIATED COLD FRONT IS FORECAST TO DROP
INTO THE SOUTHERN PLAINS AT THAT TIME.  MEANWHILE...A TRAILING
MID-UPPER LEVEL SHORTWAVE IS EXPECTED TO DIVE SOUTH FROM THE
PACIFIC NORTHWEST INTO THE GREAT BASIN ON THU.  UPSLOPE FLOW IN
THE WAKE OF THE FRONT INTERACTING WITH ENHANCED UPPER DIVERGENCE
ALONG THE LEFT-EXIT REGION OF THE UPPER JET IS FORECAST TO SUPPORT
THE DEVELOPMENT OF MODERATE TO LOCALLY HEAVY SNOWS ALONG THE CO/WY
FRONT RANGE AND THE ADJACENT HIGH PLAINS.  WPC AMOUNTS FAVORED A
BLEND OF THE GFS/ECMWF.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA