Prognostic Meteorological Discussion
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FXAK02 KWNH 291836
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 PM EDT MON JUN 29 2015

VALID 12Z FRI JUL 03 2015 - 12Z TUE JUL 07 2015

DETAILS REMAIN IN DOUBT BUT GUIDANCE IS STILL SUGGESTING AN
OVERALL INCREASE IN PREDICTABILITY AS THE DOMINANT FEATURES BECOME
LARGER IN SCALE... SPECIFICALLY THE RIDGE BUILDING OVER THE NERN
PAC INTO MAINLAND ALASKA AND THE TROUGH/EMBEDDED CLOSED LOW OVER
THE ALEUTIANS.

OVER RECENT DAYS THE ENSEMBLE MEANS HAVE TENDED TO BE THE MOST
CONSISTENT SOLNS WITH THE RIDGE BUILDING OVER THE MAINLAND...
THOUGH IT HAS TAKEN UNTIL THE PAST COUPLE DAYS FOR BOTH THE MODELS
AND MEANS TO LATCH ONTO THE IDEA THAT RISING HGTS WOULD BE
SUPPORTED BY BOTH THE UPR HIGH MIGRATING EWD FROM RUSSIA AND THE
AMPLIFICATION OF THE NERN PAC RIDGE.  THE MOST NOTABLE TREND IN
THE MEANS OVER THE PAST 24-36 HRS IS TOWARD A STRONGER MAINLAND
RIDGE.  GIVEN THIS TREND AND LATEST OPERATIONAL MODEL RUNS
GENERALLY BEING STRONGER WITH THE RIDGE THAN THE ENSEMBLE MEANS...
WOULD PREFER A BLEND OF MODEL/ENSMEAN SOLNS.  THERE IS A CHANCE
THAT 00Z AND TO SOME EXTENT 06Z/12Z GFS RUNS MAY BE OVERDOING THE
TREND A BIT WHILE THE 06Z GEFS/00Z ECMWF MEANS ARE STRONGER THAN
THE 00Z NAEFS MEAN.  THEREFORE FAVOR THE 00Z ECMWF AND 06Z
GEFS/00Z ECMWF MEANS FOR DEPICTION OF THIS RIDGE.

SPECIFICS OF CNTRL PAC/ALEUTIANS EVOLUTION CONTINUE TO BE
PROBLEMATIC.  THERE IS STILL A FAIR AMOUNT OF SPREAD AND
VARIABILITY/TRENDING WITH A LEADING SYSTEM THAT SHOULD BE NEAR OR
JUST S OF 50N LATITUDE AS OF 12Z FRI... ALONG WITH HOW ENERGY
IMMEDIATELY UPSTREAM WILL EVOLVE AND PSBLY INTERACT WITH THIS
INITIAL FEATURE.  PRIMARY TRENDS OVER THE PAST DAY HAVE BEEN TO
THE N WITH THE LEADING SYSTEM.  ENSEMBLE MEANS HAVE TENDED TO BE
MORE STABLE WITH THE SECOND SYSTEM THAT SHOULD REACH THE ALEUTIANS
BY LATE IN THE WEEKEND.  LATEST GFS RUNS ARE WEAKER/LESS
CONSOLIDATED AT THE SFC RELATIVE TO ENSMEAN CONTINUITY AND ECMWF
RUNS... THOUGH THEY STILL SHOW THE SIGNAL OF AN ENHANCED SFC
GRADIENT OVER THE ERN ALEUTIANS/WRN PENINSULA.  THE 00Z CMC IS
FAIRLY CLOSE TO THE ECMWF IN PRINCIPLE.  THESE CONSIDERATIONS
ALLOW FOR A BLEND OF 00Z ECMWF/ECMWF MEAN AND 06Z GFS/GEFS MEAN
SOLNS TO DEAL WITH UNRESOLVED DETAIL ISSUES INTO DAY 5 SAT...
FOLLOWED BY PRIMARY EMPHASIS ON THE ECMWF/ECMWF MEAN FOR THE REST
OF THE FCST.

THE AFOREMENTIONED BLEND EARLY IN THE PERIOD PROVIDES A GOOD
INTERMEDIATE FCST FOR THE MODEST SHRTWV CROSSING THE MAINLAND
BEFORE RIDGING BUILDS IN... AND THEN LATER IN THE PERIOD 06Z GEFS
WEIGHTING THAT IS INCLUDED FOR THE MAINLAND RIDGE IS STILL NOT
SUFFICIENTLY GREAT TO HAVE AN ADVERSE INFLUENCE ON THE MORE
FAVORED 00z EC/EC MEAN OVER THE ALEUTIANS.

RAUSCH

$$





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