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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1756Z Aug 17, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 PM EDT SUN AUG 17 2014

VALID 12Z THU AUG 21 2014 - 12Z MON AUG 25 2014

ENSEMBLE MEANS AND THE ECMWF MEAN IN PARTICULAR HAVE MAINTAINED
GOOD CONTINUITY WITH THE EXPECTED LARGE SCALE PATTERN... SO EXPECT
ONLY MODEST ADJUSTMENTS IN TODAY'S FORECAST.

WITHIN THE AGREED UPON BERING SEA INTO CNTRL PAC MEAN TROUGH THERE
IS STILL REASONABLE CONSENSUS TOWARD AN EMBEDDED UPR LOW THAT
SHOULD DRIFT TO THE E/NE.  OVERALL A MAJORITY OF LATEST GUIDANCE
HAS TRENDED A LITTLE WEAKER WITH SFC DEVELOPMENT FROM THE
ALEUTIANS INTO BERING SEA... OR AT LEAST IS TAKING LONGER TO
STRENGTHEN THE SYSTEM.  THIS REFLECTS SOMEWHAT LESS ENERGETIC
INTERACTION OF UPSTREAM MID-LATITUDE PAC FLOW AND THE INITIAL UPR
SYSTEM NEAR THE ALEUTIANS.  A COMPROMISE AMONG THE 00Z GFS/ECMWF
AND 06Z GEFS/00Z ECMWF MEANS LOOKS REASONABLE THROUGH DAY 6 SAT
WITH MOST WEIGHTING TOWARD THE MEANS THEREAFTER AS CONFIDENCE IN
OPERATIONAL MODEL DETAILS DECLINES.  PREFER TO KEEP WEIGHTING OF
THE TWO MEANS RELATIVELY EVEN TO TAKE ADVANTAGE OF ECMWF MEAN
STABILITY/VERIFICATION AND BETTER SFC LOW DEFINITION IN THE 06Z
GEFS MEAN.  06Z/12Z GFS RUNS MAY BECOME SOMEWHAT FAST WITH LEADING
HGT FALLS LATE IN THE PERIOD.

LATEST SOLNS ARE STILL NOT AGREEABLE WITH THE STRENGTH OF SHRTWV
ENERGY ROUNDING THE DOWNSTREAM RIDGE AND ASSOC SFC DEPICTION
OFFSHORE THE SRN COAST LATE THIS WEEK INTO THE WEEKEND.  WITH THE
00Z CMC NOW STRONGER WITH THE RIDGE ALOFT AS PER CONSENSUS... THE
00Z ECMWF IS MOST PRONOUNCED WITH ENERGY ALOFT AND ASSOC SFC
WAVINESS.  STRENGTH OF THE RIDGE ALOFT STILL APPEARS TO FAVOR
WEAKER ENERGY ALOFT THAN FCST BY THE 00Z ECMWF AND A SFC FRONT
WITH MERELY A HINT OF WAVINESS LIFTING NWD TOWARD THE SRN COAST.

FINALLY THERE IS SOME SPREAD WITH NRN STREAM FLOW INITIALLY W OF
THE NRN MAINLAND.  TELECONNECTIONS RELATIVE TO THE CORE OF
POSITIVE ANOMALIES FCST TO BE NEAR 50N 140W IN THE D+8 MULTI-DAY
MEANS SUGGEST SOME DEGREE OF MEAN RIDGING EXTENDING WELL NWD
THROUGH THE MAINLAND.  THIS IDEA IS CONSISTENT WITH THE ENSEMBLE
MEANS.  HAVING THE NRN STREAM ENERGY REMAIN TO THE W OF THE NRN
MAINLAND AS IN THE 00Z GFS OR BE WEAK/PROGRESSIVE AS IN THE 00Z
ECMWF ARE THE MOST PLAUSIBLE OPERATIONAL SOLNS.  THE 06Z GFS IS
LEAST FAVORED AND 12Z GFS DETAILS DIFFER FROM MOST OTHER SOLNS.

OVER BOTH OF THESE LATTER TWO AREAS THE BLEND DESCRIBED FOR THE
ALEUTIANS/BERING SEA SYSTEM REPRESENTS THE DESIRED CONSENSUS
SFC/ALOFT... WITH SUFFICIENTLY SMALL WEIGHTING OF THE 00Z ECMWF TO
MINIMIZE INFLUENCE ON NERN PAC DETAILS.

RAUSCH