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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1834Z Dec 18, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
134 PM EST THU DEC 18 2014

VALID 12Z MON DEC 22 2014 - 12Z FRI DEC 26 2014

LATEST GUIDANCE MAINTAINS BETTER THAN AVERAGE CONTINUITY AND
AGREEMENT WITH THE MOST SIGNIFICANT ASPECTS OF THE FCST.  A
GRADUALLY WEAKENING SHRTWV TROUGH CONSISTING OF MULTIPLE PIECES OF
ENERGY SHOULD PROGRESS ACROSS THE MAINLAND AND NERN PACIFIC.  A
DEEP UPR LOW IN THE MEAN SHOULD SETTLE OVER KAMCHATKA WITH RIDGING
BUILDING DOWNSTREAM OVER OR NEAR THE MAINLAND/NERN PAC TO REPLACE
THE INITIAL SHRTWV.  SFC LOW PRESSURE INITIALLY OFF THE SRN COAST
WILL WEAKEN CORRESPONDING TO THE PROGRESSION/FILLING OF THE SHRTWV
ALOFT... LIKELY LOSING DEFINITION BY 12Z WED.  SOME SFC TROUGHING
IS LIKELY TO REMAIN NEAR THE COAST/PANHANDLE THOUGH.  MEANWHILE
MOST OPERATIONAL MODEL SOLNS ARE MAINTAINING THE IDEA THAT A
STRONG BUNDLE OF ENERGY ROUNDING THE KAMCHATKA MEAN LOW WILL
SUPPORT A VERY DEEP WRN BERING SEA SFC LOW AROUND TUE-WED. 
PERSISTENCE OF THIS SCENARIO IN MODEL RUNS AND IMPROVED CLUSTERING
FOR TIMING/TRACK... ASIDE FROM THE 12Z GFS THAT HAS JUMPED EWD...
LEAD TO HIGHER CONFIDENCE IN A SOLN THAT LEANS AT LEAST 2/3 TOWARD
OPERATIONAL GUIDANCE RATHER THAN THE WEAKER ENSEMBLE MEANS THAT
HAVE EITHER BEEN STABLE OR TRENDING A LITTLE STRONGER OVER THE
PAST COUPLE DAYS.  THIS SYSTEM WILL BRING A FAST MOVING FRONT
ACROSS THE ALEUTIANS/BERING SEA.  BY DAY 8 FRI THERE ARE
REASONABLE SIGNALS THAT UPSTREAM ENERGY REACHING THE WRN PAC MAY
GENERATE ANOTHER SFC LOW AFFECTING THE WRN ALEUTIANS.

DAYS 4-6 MON-WED ARE WEIGHTED 70 PCT TOWARD THE 06Z GFS/PARALLEL
GFS AND 00Z ECMWF WITH THE REST 06Z GEFS MEAN/00Z ECMWF MEAN TO
GIVE THE DESIRED APPROX 2/3 EMPHASIS ON OPERATIONAL GUIDANCE FOR
THE DEEP WRN BERING SEA SFC LOW.  FOR SFC LOW PRES OFF THE SRN
COAST AS OF EARLY DAY 4... THE RESULTING BLEND YIELDS A GOOD
INTERMEDIATE SOLN RELATIVE TO THE SOLN SPREAD AND IN PARTICULAR IS
TO THE NE OF THE 00Z ECMWF.  DAYS 7-8 THU-FRI ADJUST TO A MORE
EVEN BLEND OF OPERATIONAL/ENSEMBLE MEAN SOLNS GIVEN MODEL DETAILS
THAT HAVE LESS CONFIDENCE AT THAT TIME FRAME BUT ARE STILL CLOSE
ENOUGH TO THE MEANS TO MERIT PARTIAL WEIGHTING.

RAUSCH