Prognostic Meteorological Discussion
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FXAK02 KWNH 171838
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
138 PM EST WED DEC 17 2014

VALID 12Z SUN DEC 21 2014 - 12Z THU DEC 25 2014

THE GENERAL THEME OF THE FCST IS LITTLE CHANGED FROM 24 HRS AGO.
A CLOSED OR NEARLY CLOSED UPR LOW NEAR THE ALASKA PENINSULA SHOULD
OPEN UP EARLY IN THE PERIOD AS UPSTREAM TROUGH ENERGY
APPROACHES... WITH THE OVERALL TROUGH WEAKENING WHILE IT
PROGRESSES EWD AS A DEEP UPR LOW SETTLES OVER THE VICINITY OF
KAMCHATKA.  INDIVIDUAL MODEL/ENSEMBLE MEMBER DETAILS DIFFER BUT
THE ENSEMBLE MEANS AS A WHOLE AGREE QUITE WELL THAT THIS FEATURE
SHOULD ULTIMATELY SUPPORT THE BUILDING OF A RIDGE WHOSE AXIS
SHOULD LIE OVER/NEAR THE ERN MAINLAND BY DAY 8 NEXT THU.

INITIAL PREFS FOR THE DAYS 4-8 SUN-THU PERIOD EMPHASIZE THE 00Z
ECMWF MEAN WITH MINORITY INPUT FROM THE 00Z ECMWF/12Z GFS.  EARLY
IN THE PERIOD THIS BLEND EMPHASIZES THE GREATER PREDICTABILITY OF
THE LARGER SCALE PATTERN EXPECTED AT THE TIME... AS INDIVIDUAL
SOLNS ARE STILL HAVING DIFFICULTY RESOLVING SMALL SCALE SHRTWV/SFC
DETAILS.  00Z ECMWF WEIGHTING IS SUFFICIENTLY SMALL TO DOWNPLAY
ITS COMPACT WAVE OFF THE PANHANDLE/SERN COAST ON SUN.  MOST
GUIDANCE CLUSTERS BETTER BY MON-TUE AS SFC LOW PRESSURE IS FCST TO
WEAKEN IN PLACE JUST OFF THE KENAI PENINSULA.  UPSTREAM
SIGNIFICANT TIMING/TRACK DIFFS EMERGE IN FLOW AHEAD OF THE DEEP
UPR LOW IN THE MEAN NEARING KAMCHATKA.  PREFER TO MAINTAIN SLOWER
TIMING/WWD SFC LOW TRACK VERSUS 00Z-06Z OPERATIONAL GFS/GEFS SOLNS
OVER THE BERING SEA... WITH SUPPORT FROM THE PARALLEL GFS RUNS.
THE 12Z GFS HAS FAVORABLY ADJUSTED TO THIS SLOWER SCENARIO.  IT
REMAINS TO BE SEEN WHETHER THE DEEP SYSTEM OVER THE WRN BERING SEA
REACHES A CNTRL PRES AS LOW AS THE 00Z ECMWF/12Z GFS BUT ADDING 20
PCT OF EACH HELPS TO STRENGTHEN THE ECMWF MEAN BASE SOMEWHAT IN
LIGHT OF THE OVERALL NUMBER OF OPERATIONAL SOLNS SHOWING A DEEPER
SYSTEM THAN THE ENSEMBLE MEANS.

RAUSCH

$$





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