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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1849Z Oct 25, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT SAT OCT 25 2014

VALID 12Z WED OCT 29 2014 - 12Z SUN NOV 02 2014

THE MOST SIGNIFICANT CHANGE IN THE GUIDANCE OVER THE PAST 24 HRS
IS A TREND TOWARD MORE OF A RIDGE DRIFTING FROM ERN SIBERIA TO THE
NRN COAST OF THE MAINLAND OR A LITTLE N/W.  THIS LATEST EVOLUTION
RESULTS IN A CONSIDERABLY MORE SUPPRESSED TRACK FOR THE SYSTEM
EXPECTED TO BE NEAR KAMCHATKA EARLY IN THE PERIOD AND PROGRESS EWD
THEREAFTER... THOUGH THE 00Z CMC ENSEMBLE MEAN STILL HAS A VESTIGE
OF THE EARLIER CLUSTERING THAT HAD SHOWN A NRN BERING SEA TRACK. 
SFC PRESSURES ARE NOTICEABLY HIGHER OVER THE NRN MAINLAND.  BEHIND
THIS SYSTEM DETAILS WILL BE DIFFICULT TO RESOLVE IN THE FRI-SAT
TIME FRAME GIVEN MODEST AMPLITUDE OF EMBEDDED FEATURES. 
MODELS/ENSEMBLES THEN HINT AT A DEVELOPING ERN ASIA TROUGH AND
APPROXIMATE 170E RIDGE/160W TROUGH CONFIGURATION BY 00Z AT THE END
OF DAY 8 NEXT SUN.

OVER THE NERN PAC THERE IS STILL A DECENT AMOUNT OF SPREAD WITH
INDIVIDUAL MODEL/ENSEMBLE MEMBER LOW POSITIONS AT ANY PARTICULAR
VALID TIME.  IN SPITE OF THESE DIFFS THERE IS SOME SEMBLANCE OF
CONTINUITY IN A VERY BROAD SENSE.  THE GENERAL IDEA IS FOR THE LOW
SFC/ALOFT TO THE SE OF KODIAK ISLAND AS OF EARLY DAY 4 WED TO
ELONGATE SEWD AND THEN ROTATE N/NW SOME DISTANCE OFFSHORE OR JUST
S OF THE PANHANDLE... WHETHER THE SAME LOW OR A NEW DEVELOPMENT
REMAINS TO BE SEEN... BEFORE EITHER WEAKENING AS IT COMES ASHORE
OR MERGING WITH ENERGY ON THE LEADING EDGE OF THE SYSTEM FCST TO
TRACK ACROSS THE SRN BERING SEA.  IN ADDITION THE POSSIBILITY
EXISTS FOR THE NERN PAC MEAN LOW TO INCORPORATE SOME PORTION OF
THE SYSTEM ASSOC WITH EXTRATROPICAL ANA/SHORT RANGE INTERACTION
WITH A MID-LATITUDE PAC WAVE.

LACK OF CONFIDENCE IN EXACT DETAILS OVER THE NERN PAC FAVORS AN
ENSEMBLE MEAN EMPHASIS BY WAY OF THE 06Z GEFS/00Z ECMWF MEANS...
WHILE 00Z-06Z GFS/00Z ECMWF RUNS PROVIDE SOME BETTER DETAIL WITH
THE BERING SEA SYSTEM THU-FRI.  BY SAT THE 06Z GFS IS MORE LIKE
THE 00Z ECMWF/ECMWF MEAN WITH THE SFC LOW TO THE E OF KODIAK
ISLAND AT THAT TIME VERSUS THE MUCH FARTHER SWD 00Z GFS.  THE
COMBINATION OF THESE CONSIDERATIONS YIELDS A STARTING BLEND
COMPOSED OF 70 PCT OF THE AFOREMENTIONED MEANS AND THE REMAINDER
FROM THE OPERATIONAL 06Z GFS/00Z ECMWF.  EXPECTED DETAIL DIFFS
ARISE IN 12Z GUIDANCE... WITH THE 12Z GFS NOTABLY FAST WITH THE
BERING SEA SYSTEM FOR A TIME AROUND FRI... BUT THE NEW SOLNS AS A
WHOLE AT LEAST MAINTAIN CURRENT CONFIDENCE LEVELS IN THE MANUAL
FCST.  

RAUSCH