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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1858Z Oct 20, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT MON OCT 20 2014

VALID 12Z FRI OCT 24 2014 - 12Z TUE OCT 28 2014

THE ALASKA MEDIUM RANGE FORECAST MAINTAINED THE 20/00Z ECENS MEANS
APPROACH...AND THE SLIGHTLY FASTER 20/00Z NAEFS MEANS FOR THE FLOW
PATTERN OVER ALASKA AND THE CENTRAL PACIFIC. THIS ALLOWS THE
NORTHERN...HIGH LATITUDE FLOW TO PROGRESS ACROSS THE BERING SEA
AND REPLENISH THE NORTHERNMOST PORTION OF THE GULF OF ALASKA WITH
A MODIFIED-ARCTIC AIRMASS...WEAK CYCLONIC SURFACE FLOW AND BROAD
WEST TO NORTHWEST FLOW ALOFT.

THAT IS A KEY FEATURE OF THIS MEDIUM RANGE FORECAST
PHILOSOPHY---LIMITING THE ABILITY OF SUBTROPICAL MOISTURE TO REACH
THE NORTH CENTRAL GULF...MAINTAIN A MORE AMPLIFIED FLOW PATTERN IN
THE NORTH CENTRAL PACIFIC...AND MORE IMPORTANTLY---DIRECT THE BULK
OF THE TROPICAL CONNECTION AND MOISTURE INTO SOUTHWEST CANADA AND
POINTS SOUTH.

OF NOTE...
AS EARLY AS DAY 5...THE 20/12Z DETERMINISTIC RUNS
(ECMWF-GFS-CANADIAN) HAVE SOME DIFFERENCES BETWEEN 160W-170W AND
35N-45N WITH THE NATURE OF THE SURFACE PATTERN AS 'ANA' BECOMES
ENTRAINED IN THE MID-LATITUDE WESTERLY FLOW. BY DAY 7...THE
GFS...ECMWF AND CANADIAN CARRY A SIGNIFICANT SHORTWAVE ALONG
135W...BUT THAT IS ABOUT ALL THAT THEY HAVE IN COMMON.
SPEED...DEPTH AND TRAJECTORY...ALL POINTING TO HAVING AN ENSEMBLE
MEAN SOLUTION FOR DAY 6-8 IN THE EAST CENTRAL AND NORTHEAST
PACIFIC BASINS.

VOJTESAK