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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1803Z Oct 19, 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
203 PM EDT SUN OCT 19 2014

VALID 12Z THU OCT 23 2014 - 12Z MON OCT 27 2014


THE ALASKA MEDIUM RANGE FORECAST CONTINUED TO SHOW PROGRESSION OF
THE UPPER-LEVEL FLOW PATTERN AT HIGH LATITUDE---WITH LARGE SPREAD
DEVELOPING OVER NORTHEAST SIBERIA AND THE NORTHERN BERING SEA. THE
19/00Z ECENS MEANS AND 19/00Z GEFS MEANS OFFERED A DECENT
COMPROMISE---AND IN COORDINATION WITH THE ANCHORAGE EXTENDED
DESK---SET THE PATTERN PROGRESSION WITH A 70/30 RATIO OF
ECENS/GEFS MEANS AS A BASELINE FOR THIS FORECAST.

DOWNSTREAM...THE SCENARIO FOR A 'SPLIT-FLOW' TO DEVELOP ALONG 140W
LONGITUDE SERVES THE ON-GOING CONTINUITY...CURRENT BLEND AND
FORECAST WELL---TRENDING FOR DRIER CONDITIONS ALONG THE PACIFIC
COAST/GULF OF ALASKA.

THE FLOW PROGRESSION THAT DOES OCCUR AFTER DAY 5 TENDS TO FOCUS IN
THE BERING SEA RATHER THAN THE GULF OF ALASKA---WITH A BROAD
TROUGH EMERGING OFF THE KAMCHATKA PENINSULA AND NORTHEASTERN
SIBERIA. THE 19/00Z GFS/ECMWF/CANADIAN DETERMINISTIC RUNS LOOKED
REASONABLE WITH THE MID-LATITUDE WESTERLIES MOVING ACROSS EAST
CENTRAL CHINA AND DOWNSTREAM TO THE DATELINE. BUT DIFFER IN THE
INDIVIDUAL SHORTWAVE STRENGTH AND TRAJECTORY EXITING NORTHEAST
ASIA...SO AN ENSEMBLE MEAN APPROACH SEEMS APPROPRIATE.  

IN THE CENTRAL PACIFIC...THE LEFTOVER ENERGY/VORTICITY AND
MOISTURE FROM 'ANA' INVOF KAUAI HAVE CREATED SUBSTANTIAL
RUN-TO-RUN ERRORS. A BLEND OF THE 19/00Z GEFS/ECENS MEANS HAS
LIMITED SUCCESS IN PINPOINTING THE ENTRY POINT AND TIMING OF THIS
TROPICAL SYSTEM'S EXIT AND ENTRAINMENT INTO THE MID-LATITUDES AND
THE WESTERLY FLOW ALOFT.  AFTER COORDINATING A POINT NEAR 38N 160W
AT DAY 7 WITH THE CPHC...IT'LL SERVE AS A DECENT STARTING POINT TO
MONITOR FOR DOWNSTREAM CHANGES IN THE FUTURE. BASED ON THE CURRENT
500MB GRAPHICS AND THE CPHC POSITION (26/12Z)...THE SYSTEM IS NOT
A CONCERN FOR THE GULF OF ALASKA ON DAYS 7-8.

VOJTESAK