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575
FXAK02 KWNH 231800
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EDT WED APR 23 2014

VALID 12Z SUN APR 27 2014 - 12Z THU MAY 01 2014

MODELS AND ENSEMBLES APPEAR TO HAVE CONVERGED ON MOST ASPECTS OF
THE FCST EARLY IN THE PERIOD OVER/NEAR THE MAINLAND AND NERN
PAC... WITH MODEST RIDGING ALOFT FROM NWRN CANADA INTO THE
MAINLAND WHILE A DEEP LAYER LOW SETTLES OVER THE NERN PAC.  BY DAY
5 MON THE 00Z GFS IS THE ONE PIECE OF GUIDANCE AT ODDS WITH
CONSENSUS AS IT BRINGS THE LOW FARTHER N/NE.  THEN BY TUE THE 00Z
GFS BECOMES MORE WRAPPED UP THAN OTHER SOLNS WITH ENERGY ON THE
SERN SIDE OF THE UPR LOW/TROUGH.  THERE REMAINS POTENTIAL FOR
SHRTWV ENERGY ROUNDING THE SRN/ERN SIDE OF THIS FEATURE TO PROMOTE
A WEAK SFC WAVE/TROUGH OFFSHORE THE PANHANDLE/SERN COAST AROUND
THE MIDDLE OF THE PERIOD.

CONFIDENCE IN DETAILS OF UPSTREAM EVOLUTION FROM THE WRN PAC INTO
THE BERING SEA REMAINS AT OR BELOW AVG GIVEN EXPECTED STREAM
INTERACTION.  THE ONE POSITIVE TREND FROM 24 HRS AGO IS A
PRONOUNCED ADJUSTMENT OF GFS/GEFS SOLNS TOWARD THE ECMWF MEAN IDEA
OF SHOWING GREATER EMPHASIS ON NRN STREAM LOW PRES TRACKING INTO
THE BERING SEA AND HAVING THE NEWD-MOVING WRN PAC SYSTEM MERGE
WITH OR REINFORCE THE BERING SEA LOW.  THE 12Z GFS TRACKS THE WRN
PAC LOW TO THE S OF THE ALEUTIANS/AK PENINSULA WHILE THE PAST
COUPLE ECMWF RUNS ARE SUFFICIENTLY AMPLIFIED/CLOSED WITH TRAILING
NRN STREAM ENERGY TO HOLD BACK A SFC LOW OVER OR S OF THE WRN
ALEUTIANS LATE IN THE PERIOD.  THESE ARE CONSIDERED LESS LIKELY
SCENARIOS AT THIS TIME.  SLOWER TRENDS IN THE ECMWF MEAN OVER THE
PAST COUPLE DAYS SUGGEST THAT LATEST GFS AND GEFS/CMC MEAN RUNS
COULD BE SOMEWHAT FAST WITH EWD PROGRESSION OF HGT FALLS
ALOFT/LOWER SFC PRESSURES.  HOWEVER PREFER TO LEAN ONLY 2/3 TOWARD
THE ECMWF MEAN AS FLATTENING MID-LATITUDE PAC FLOW COULD PULL AT
LEAST THE SRN PART OF THE ALEUTIANS/BERING SEA MEAN UPR LOW A
LITTLE FARTHER EWD.

CONSENSUS OVER THE MAINLAND/NERN PAC EARLY IN THE PERIOD COMBINED
WITH CONSIDERATIONS UPSTREAM LEAD TO STARTING DAYS 4-5 SUN-MON
WITH A BLEND OF 12Z GFS/00Z ECMWF RUNS AND 00Z ECMWF/00Z NAEFS/06Z
GEFS MEANS WITH SOMEWHAT HIGHER WEIGHTING TO THE ECMWF/ECMWF MEAN.
 AS OPERATIONAL DETAILS BECOME MORE UNCERTAIN THEREAFTER... THE
BLEND ADJUSTS TO 70/20/10 WEIGHTINGS OF THE 00Z ECMWF MEAN/00Z
NAEFS MEAN/06Z GEFS MEAN.

RAUSCH

$$





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