Prognostic Meteorological Discussion
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FXAK02 KWNH 011816
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 PM EDT WED APR 01 2015

VALID 12Z SUN APR 05 2015 - 12Z THU APR 09 2015

AT LEAST FOR THE MOMENT THE LATEST GUIDANCE SHOWS BETTER AGREEMENT
WITH THE MOST SIGNIFICANT FEATURES COMPARED TO RECENT DAYS...
AIDED BY RECENT ECMWF MEAN TRENDS AND SLIGHT ADJUSTMENTS IN OTHER
SOLNS.

ALBEIT WITH SOME LINGERING SPREAD THERE IS BETTER CONSENSUS TOWARD
SHORT RANGE BERING SEA/ALEUTIANS ENERGY SUPPORTING A WEAK WAVE
JUST E OF KODIAK ISLAND AS OF 12Z DAY 4 SUN.  THIS IS IN LINE WITH
YDAYS PREFERENCES.  AN AVG OF MODEL/ENSEMBLE MEAN FCSTS IS
REASONABLE FOR THIS FEATURE... THOUGH WITH LOW ENOUGH MODEL
WEIGHTING TO DOWNPLAY GFS STRENGTH FOR THE NERN PAC WAVE AS WELL
AS RESIDUAL 00Z ECMWF LOW PRES OVER THE ERN BERING SEA.

UPSTREAM FOCUS WILL BE DOMINATED BY TWO BERING SEA SYSTEMS.  THE
ENSEMBLE MEANS ARE IN REMARKABLY GOOD AGREEMENT THROUGH DAY 6 TUE
FOR THE FIRST ONE... WITH TIMING SLIGHTLY SLOWER THAN YDAYS
CONTINUITY AT SOME FCST HRS... WHILE THERE IS SOME SPREAD FOR
TIMING BUT LESS SO FOR TRACK WITH THE SECOND.  THE 00Z ECMWF
STRAYS TO THE SE OF CONSENSUS WITH THE UPR LOW ASSOC WITH THE
FIRST SYSTEM AS EARLY AS DAY 5 MON.  THE 00Z NAEFS MEAN IS THE
FASTEST AMONG THE ENSMEANS WITH THE SECOND SYSTEM... WHICH LEADS
TO SLIGHTLY EARLIER WEAKENING OF THE LEADING SYSTEM.  OPERATIONAL
MODELS OFFER POTENTIAL FOR THE TRAILING SYSTEM TO BE SLOWER THAN
EVEN THE 06Z GEFS/00Z ECMWF MEANS SO WOULD AT LEAST FAVOR
EXCLUDING THE FASTER NAEFS MEAN FROM THE FCST.  HOWEVER WITH
OPERATIONAL RUNS HAVING TRENDED MORE TO PRIOR MEANS FOR THE
OVERALL EVOLUTION OF THE LEADING BERING SEA SYSTEM... CONFIDENCE
IS CURRENTLY SOMEWHAT HIGHER IN THE GEFS/ECMWF MEANS.

ALOFT EXPECT HGTS TO RISE SOMEWHAT OVER THE CNTRL-NRN MAINLAND AS
AN INITIAL WEAKNESS IS REPLACED BY RIDGING EXTENDING NWWD FROM
CANADA IN ADVANCE OF THE FIRST BERING SEA SYSTEM.  SOME OF THIS
RIDGING SHOULD PERSIST AS THE TRAILING UPR LOW REACHES THE BERING
SEA.  INDIVIDUAL MODEL RUNS/ENSEMBLE MEMBERS VARY WITH DETAILS
ALOFT OVER THE MAINLAND BUT THESE DIFFS APPEAR TO HAVE ONLY MODEST
IMPACT AT THE SFC.

BASED ON THE ABOVE CONSIDERATIONS THE DAY 4 SUN FCST STARTS WITH A
60/40 WEIGHTING OF THE 06Z GEFS/00Z ECMWF MEANS VERSUS THE 06Z
GFS/00Z ECMWF.  DAYS 5-6 MON-TUE CONSIST MOSTLY OF THE 06Z
GEFS/00Z ECMWF MEANS WITH A MODEST 06Z GFS COMPONENT REMAINING.
THE 12Z GFS CHANGES ARE FAIRLY MODEST SO IT COULD BE SUBSTITUTED
FOR THE 06Z RUN.  PREFS TO LEAN AWAY FROM THE NAEFS MEAN LATER IN
THE PERIOD AND DECREASING CONFIDENCE IN ANY PARTICULAR OPERATIONAL
SOLN LEAD TO AN EVEN WEIGHTING OF THE 06Z GEFS/00Z ECMWF MEANS BY
DAYS 7-8 WED-THU.

RAUSCH

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