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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1829Z Apr 15, 2014)
 
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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
229 PM EDT TUE APR 15 2014

VALID 12Z SAT APR 19 2014 - 12Z WED APR 23 2014

MEDIUM RANGE PATTERN CONTINUES TO FEATURE A BROAD TROUGH IN THE
GULF OF ALASKA AND A RIDGE OVER THE NORTHERN INTERIOR. THE BROAD
TROUGH AND CYCLONIC FLOW IN THE GULF OF ALASKA WILL BE RIDDLED
WITH SHORTWAVE ENERGY...AND THE LATEST 15/00Z GUIDANCE DEPICTS A
RELATIVELY WET PATTERN FOR PORTIONS OF THE PANHANDLE AND THE
SOUTHERN COAST LINE.

THE WPC GRAPHICS WERE GENERALLY INTACT FOR THE NEW DAY 4 THROUGH
DAY 8 WITH SOME MANUAL MODIFICATIONS. THE FORECAST PHILOSOPHY
TODAY: FOLLOW THE 15/00Z ECENS MEANS...WHICH HAS BEEN CONSISTENT
WITH THE COMPLEX TROUGH/RIDGE CONFIGURATION ACROSS THE HIGH
LATITUDE PACIFIC. CONCERNING INDIVIDUAL SHORTWAVE DETAILS...USED
ASPECTS OF THE DETERMINISTIC ECMWF AND CANADIAN...THOUGH TIMING
WILL CONTINUE TO BE A SHORTER RANGE ISSUE IN THE NORTHERN GULF AND
ALONG THE SOUTH COAST AND ENTIRE PANHANDLE.

NOT SURE ALL THE FEATURES DEPICTED ON THE SURFACE GRAPHICS
(SNAPSHOTS AT 12Z EACH DAY) WILL ACCURATELY DISPLAY THE COMPLEXITY
OF THE SHORTWAVE DETAIL AND FRONTAL STRUCTURE...GIVEN THE VERY
LARGE SPREAD IN THE 15/00Z GUIDANCE PACKAGES.

THE 15/00Z GEFS...ECENS MEAN AND CANADIAN ENSEMBLE MEAN WERE IN
DECENT AGREEMENT ALOFT THROUGH DAY 5...BEFORE THE GEFS MEAN BREAKS
WITH THE PACK AND CONTINUITY...EJECTING A STRONG SHORTWAVE FROM
THE PARENT CYCLONIC FLOW IN THE SOUTHERN GULF...EAST-SOUTHEASTWARD
TOWARDS THE OREGON/CALIFORNIA COAST. THIS GEFS SOLUTION BEGINS THE
PROCESS AROUND 21/00Z AND PINCHES OFF A CLOSED 500MB LOW THAT
ARRIVES ALONG THE WEST COAST ALMOST AN ENTIRE DAY (24 HOURS)
EARLIER FOR THE DAY 6-7 PERIOD VERSUS THAN THE CANADIAN AND ECMWF
SOLUTIONS. LIKEWISE...THE 15/00Z GEFS MEAN IS A GOOD 10-15 DEGREES
OF LONGITUDE FASTER WITH THE EASTWARD MIGRATION OF A SECONDARY
UPPER-LEVEL TROUGH MOVING THROUGH THE ALEUTIANS AFTER DAY 5. THIS
SECONDARY TROUGH APPEARS TO REJUVENATE THE CYCLONIC FLOW ANCHORED
IN THE GULF.

THE DETERMINISTIC 15/06Z GFS HELD TO THIS FASTER FLOW PROGRESSION
AND BOTH 15/00Z AND 15/06Z VERSIONS OF THE GFS PRODUCT SUITE WERE
ELIMINATED FROM THE MIX. WITH BETTER OVERALL AGREEMENT BETWEEN THE
15/00Z DETERMINISTIC CANADIAN AND ECMWF...USED THESE PIECES OF
GUIDANCE FOR SOME OF THE DETAILS OVER THE ALEUTIANS FOR A SLOWER
PROGRESSION OF THE SECONDARY TROUGH. THOUGH THEIR INDIVIDUAL
DETAILS DOWNSTREAM BETWEEN DAY 4-6 IN THE NORTHERN GULF OF
ALASKA...WERE LESS THAN STELLAR...CHOSE THESE DETAILS OVER THE GFS
VERSION(S).

DO EXPECT ENERGY WILL CONTINUE TO UNDERCUT THE RIDGE...DIRECTING
PACIFIC MOISTURE PRIMARILY INTO BC AND THE SOUTHERN PANHANDLE.
HOWEVER...THE PRESENCE OF A BROAD AND 'RELOADING' CYCLONIC FLOW IN
THE NORTH CENTRAL GULF OF ALASKA WILL ALLOW THE GRADUAL 'POLEWARD'
EROSION OF THE UPWIND SIDE OF THE RIDGE AXIS--INVOF SOUTH CENTRAL
ALASKA AND THE NORTHERN PORTION OF THE ALASKAN PANHANDLE. BUT THE
RIDGE ESSENTIALLY REMAINS INTACT ACROSS THE NORTH...AND WHERE A
VERY DRY AND COOLER AIR MASS DOMINATES...SEEMINGLY TO BE MORE OF A
'PERSISTENCE' FORECAST THROUGH THIS MEDIUM RANGE PERIOD.

VOJTESAK