Prognostic Meteorological Discussion
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FXAK02 KWNH 021849
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM EDT TUE SEP 02 2014

VALID 12Z SAT SEP 06 2014 - 12Z WED SEP 10 2014

THE DOMINANT FOCUS THIS PERIOD WILL BE A STRONG NRN PACIFIC SYSTEM
THAT BEST CONSENSUS EXPECTS TO TRACK NEAR THE ALEUTIANS AND TOWARD
PORTIONS OF THE MAINLAND.  OVER THE PAST COUPLE DAYS
MODEL/ENSEMBLE GUIDANCE HAS ALL SHOWN A PRONOUNCED STRONGER TREND
WITH THIS SYSTEM THOUGH OPERATIONAL GFS/ECMWF RUNS CAUGHT ONTO
BETTER DEFINITION IN EARLIER RUNS THAN THE MEANS.  BEYOND SOME
TIMING SPREAD SEEN INTO MON... WITH THE 00Z ECMWF ON THE SLOWER
SIDE BUT STILL WITHIN THE FULL ENSEMBLE SPREAD... AMPLIFICATION OF
UPSTREAM SIBERIAN FLOW ADDS ANOTHER ELEMENT OF UNCERTAINTY BY DAYS
6-8 MON-WED.  GFS/EC CONTINUITY ALONG WITH 06Z GFS AND 00Z EC/CMC
RUNS SUGGEST THE 00Z GFS AMPLIFIES ITS NRN STREAM FLOW TOO FAR
EWD.  ENSEMBLE MEANS DO NOT AMPLIFY THIS ENERGY AS FAR WWD AS THE
06Z GFS CLUSTER BUT MERIT CONSIDERABLE WEIGHTING GIVEN THEIR
BETTER THAN AVG AGREEMENT THROUGH DAY 8 AND GOOD CONTINUITY
RELATIVE TO YDAYS WPC FCST.

AHEAD OF THIS EVOLUTION A COMBINATION OF NERN PAC AND MAINLAND
SHRTWVS SHOULD SUPPORT A SFC WAVE NEAR THE SRN/SERN COAST SAT-SUN.
 FOR THIS PART OF THE FCST THE 00Z GFS COMPARES POORLY TO OTHER
GUIDANCE ALOFT AND TO SOME DEGREE AT THE SFC OVER THE SERN
MAINLAND/PANHANDLE.

BASED ON THE ABOVE GUIDANCE COMPARISONS THE DAYS 4-8 SAT-WED FCST
EMPHASIZES THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS WITH SOME
WEIGHTING OF THE 06Z GFS INCLUDED TO ADD SOME OPERATIONAL DETAIL
IN LIGHT OF TRENDS SHOWING SOME PSBL USEFULNESS OF COMPATIBLE
RUNS.  THE 00Z ECMWF IS ALSO SUFFICIENTLY CLOSE TO CONSENSUS TO BE
INCLUDED THROUGH 12Z DAY 5 SUN.  THE 06Z GFS IS NOT AVBL AFTER DAY
7 SO DAY 8 USES THE ENSEMBLE MEANS EXCLUSIVELY.

IF ANYTHING THE NEW 12Z SOLNS LOWER CONFIDENCE IN A PARTICULAR
SCENARIO.  THE GFS PULLS OFF NRN STREAM ENERGY EVEN FARTHER WWD
THAN THE 06Z GFS/00Z ECMWF... ULTIMATELY LEADING TO AN
ALEUTIANS/BERING SEA SYSTEM CONSIDERABLY SLOWER THAN THE 00Z ECMWF
BY DAY 8 WED.  THE 12Z ECMWF REMAINS SLOW WITH THE INITIAL NRN PAC
SYSTEM AND DELAYS NRN STREAM AMPLIFICATION... RESULTING IN LEAVING
THE NRN PAC SYSTEM MUCH FARTHER SWWD THAN OTHER GUIDANCE BY NEXT
TUE.  THE 12Z CMC ENDS UP BEING SOMEWHAT OF A COMPROMISE.

RAUSCH

$$




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