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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1842Z Oct 24, 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
242 PM EDT FRI OCT 24 2014

VALID 12Z TUE OCT 28 2014 - 12Z SAT NOV 01 2014

MOST GUIDANCE IS SUGGESTING THAT THE AMPLITUDE OF MEAN FLOW SHOULD
DECREASE WITH TIME... LEADING TO BROADLY CYCLONIC FLOW WITH ANY
DISCERNIBLE TROUGH AXIS ALIGNED WEST OF THE MAINLAND. 
MODELS/ENSEMBLES APPEAR TO HAVE SORTED OUT A DECENT PORTION OF
PRIOR WIDE SPREAD WITH REGARD TO EVOLUTION OVER/S OF THE MAINLAND
EARLY IN THE PERIOD BUT THE APPROACH OF FAST FLOW FROM ASIA
CONTINUES TO KEEP CONFIDENCE FAIRLY LOW WITH UPSTREAM FEATURES.

FOR THE TROUGH EXTENDING S FROM AN UPR LOW JUST N OF THE BERING
SEA AS OF 12Z DAY 4 TUE... MORE RECENT SOLNS REPRESENT A
COMPROMISE BETWEEN SOME EARLIER GFS/GEFS RUNS THAT HAD BEEN VERY
SLOW/SHARP/AMPLIFIED AND ECMWF-ECMEAN RUNS THAT HAD BEEN QUITE
PROGRESSIVE BEFORE THE 12Z/23 CYCLE.  SFC EVOLUTION RESULTING FROM
ENERGY WITHIN THE SRN HALF OF THE TROUGH PULLING OFF INTO A CLOSED
LOW YIELDS A SFC LOW SOMEWHAT TO THE S/E OF KODIAK ISLAND BY 12Z
DAY 5 WED.  INCLUDING THE NEW 12Z RUNS THERE IS STILL A FAIR
DEGREE OF SPREAD AND RUN TO RUN CHANGES AMONG MODELS/ENSEMBLES
WITH PRECISE SFC LOW TRACK.  FURTHER SPREAD AND VARIABILITY EXIST
WITH A SEPARATE SFC LOW THAT MAY EVOLVE OFF THE PANHANDLE BY THU.

AFTER EARLY WED TIMING SPREAD INCREASES DRAMATICALLY FOR THE
SYSTEM HEADING INTO THE WRN BERING SEA AS OF THAT TIME. 
CONTINUITY AS WELL AS THE DOWNSTREAM PATTERN SUGGEST HOLDING THE
TIMING BACK RELATIVE TO THE FAST 00Z GFS/CMC/CMC MEAN.  12Z SOLNS
FAVOR TIMING AT LEAST AS SLOW AS THE SLOWER CLUSTER THROUGH THE
06Z CYCLE.  BEHIND THIS SYSTEM UPSTREAM FLOW BRINGS LOWEST
HGTS/TROUGHING INTO ERN ASIA AND THE BERING SEA.

AT LEAST FOR DAYS 4-6 TUE-THU THE 06Z GFS/00Z ECMWF AND THEIR
ASSOC ENSEMBLE MEANS PROVIDE THE MOST COMPATIBLE CLUSTERING OF
GUIDANCE ACROSS THE FCST DOMAIN AND REFLECT THE MOST CONFIDENT
CONTINUITY ADJUSTMENTS FROM PRIOR ISSUANCE ESPECIALLY OVER THE
MAINLAND AND NERN PAC.  LACK OF CONFIDENCE IN 06Z GFS SPECIFICS
NEAR THE SRN COAST FAVORS EXCLUSION OF THE 06Z GFS FROM 12Z DAY 7
FRI ONWARD... WITH THE REMAINING THREE SOLNS REMAINING IN THE
BLEND. 

RAUSCH