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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1820Z Mar 31, 2015)
 
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Abbreviations and acronyms used in this product
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT TUE MAR 31 2015

VALID 12Z SAT APR 04 2015 - 12Z WED APR 08 2015

THE MOST COMMON THEME AMONG LATEST GUIDANCE ALOFT IS AN EVOLUTION
OF THE PATTERN TOWARD NERN PAC TROUGHING WITH A PSBL
WEAKNESS/EMBEDDED UPR LOW EXTENDING NWWD ALONG OR JUST W OF THE
WRN COAST OF THE MAINLAND WHILE A MEAN RIDGE WOULD EXTEND OVER WRN
CANADA INTO THE MAINLAND.  HOWEVER INDIVIDUAL/MODEL DETAILS DIFFER
SIGNIFICANTLY THROUGH THE PERIOD AND CONTINUITY HAS BEEN LESS THAN
IDEAL.

THE FIRST CONSIDERATION OF TODAYS FCST IS TO LEAN AWAY FROM THE
00Z ECMWF MEAN FOR SOME ASPECTS OF EXPECTED EVOLUTION.  IN
PARTICULAR IT SHOWS LESS MID-LATITUDE SEPARATION ALOFT RELATIVE TO
MOST OTHER GUIDANCE NEAR OR JUST W OF 180 LONGITUDE... WHICH MAY
PLAY A PART IN THAT GUIDANCE SOURCE BEING STRONGEST WITH THE
DOWNSTREAM RIDGE.  TRENDS OVER THE PAST 1-2 DAYS IN MOST SOLNS
HAVE BEEN TOWARD LOWER HGTS/FARTHER SWD JET AXIS ACROSS THE NRN
PAC/SRN BERING SEA ALONG WITH A FARTHER SWD SFC LOW TRACK THAT
ULTIMATELY LEADS TO A CLUSTERING OF SOLNS NEAR OR S OF THE KENAI
PENINSULA/GULF OF ALASKA BY LATE IN THE PERIOD.  THERE IS ACTUALLY
SOMEWHAT BETTER AGREEMENT AT THAT POINT THAN IN SOME EARLIER FCST
HRS WHEN THERE IS STILL A DEBATE OVER WHETHER LOW PRES WILL
CONSIST OF A LEADING NRN PAC/ALEUTIANS WAVE AND PERHAPS A TRAILING
FEATURE AS PER SOME GFS/ECMWF RUNS VERSUS A MORE CONSOLIDATED
SYSTEM AS DEPICTED IN THE ENSEMBLE MEANS.

EARLY IN THE PERIOD AFOREMENTIONED TRENDS LEAD TO GREATER EWD
PROGRESSION OF ENERGY ALOFT THAT REACHES THE ERN BERING SEA AS OF
12Z DAY 4 SAT.  THE MODEST MAJORITY OF GUIDANCE SHOWS A DEFINED
SFC WAVE REACHING JUST E OF KODIAK ISLAND BY 12Z DAY 5 SUN. 
HOWEVER THIS AND OTHER BERING SEA/MAINLAND DETAILS REMAIN
UNCERTAIN EARLY IN THE PERIOD... AS REFLECTED BY MAJOR DIFFS JUST
BTWN THE 00Z/06Z AND NEW 12Z GFS RUNS.

BASED ON OBSERVED TRENDS AND GEFS/NAEFS MEAN SOLNS THAT ARE MORE
SIMILAR TO WPC CONTINUITY... COMBINED WITH POOR AGREEMENT AMONG
OPERATIONAL RUNS BOTH BTWN THEMSELVES AND THE ENSMEANS... PREFER
TO START WITH AN EVEN BLEND OF THE 06Z GEFS/00Z NAEFS MEANS TO
RESOLVE THE CURRENT SPREAD IN THE GUIDANCE.  THERE IS PLENTY OF
ROOM FOR AN ALTERNATIVE SCENARIO WITH ONE OR MORE SYSTEMS BUT AT
LEAST THIS SOLN PROVIDES DECENT STABILITY WHILE WAITING FOR ANY
ADJUSTMENTS THAT CAN BE MADE WITH SUFFICIENT CONFIDENCE.

RAUSCH