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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1759Z Apr 07, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EDT MON APR 07 2014

VALID 12Z FRI APR 11 2014 - 12Z TUE APR 15 2014

OVER THE PAST COUPLE DAYS GUIDANCE HAS BEEN COMING INTO BETTER
AGREEMENT WITH THE IDEA OF A FAIRLY STRONG MEAN RIDGE BECOMING
ESTABLISHED ACROSS THE MAINLAND AND EXTREME WRN CANADA.  TRENDS
HAVE MOSTLY BEEN IN THE DIRECTION OF ECMWF MEAN RUNS THAT HAVE
GENERALLY BEEN MORE RELUCTANT TO BRING UPSTREAM ENERGY INTO THE
RIDGE THAN GFS/GEFS RUNS WHILE DOWNPLAYING SOME OF THE MORE
EXTREME ASPECTS OF OPERATIONAL ECMWF RUNS.  THIS MEAN RIDGE SHOULD
PERSIST AS A BROAD WRN PAC SYSTEM TRACKS NEAR/INTO THE ALEUTIANS
BY THE LATTER HALF OF THE FCST PERIOD.

DURING DAYS 4-5 FRI-SAT MODELS/ENSEMBLES INDICATE A
MERGING/FILLING OF ALEUTIANS LOW PRES WITH A DEVELOPING PACIFIC
WAVE NEAR 160W LONGITUDE.  BY SAT THE CONSENSUS FROM 12Z/06 AND
NEWER GUIDANCE IS A LITTLE SLOWER THAN EARLIER FCST WITH THE
RESULTING SYSTEM AS IT TRACKS TOWARD THE SWRN ALASKA PENINSULA. 
AN ELEMENT OF UNCERTAINTY THAT REMAINS UNCHANGED FROM 24 HRS AGO
IS HOW FAR NW THIS SYSTEM TRACKS AFTER EARLY SAT... WITH
PERSISTENT SPREAD SHOWING HIGH SENSITIVITY TO THE EXACT SHAPE OF
THE RIDGE ALOFT TO THE N/E.  FOR NOW WILL MAINTAIN CONTINUITY IN A
MANNER CLOSEST TO THE ECMWF MEAN WITH A NWWD TRACK INTO THE SERN
BERING SEA AS THE SYSTEM WEAKENS... WITH ENOUGH DEEP LAYER RIDGING
DOWNSTREAM TO SUPPORT SUCH A TRACK.  A GENERAL BLEND OF ABOUT 2/3
OF THE 12Z GFS/00Z ECMWF RUNS VERSUS THE 00Z NAEFS/ECMWF MEANS
PROVIDES A GOOD STARTING POINT FOR THE FRI-SAT FCST.

FROM DAY 6 SUN ONWARD... AHEAD OF THE INITIALLY DEEP WRN PAC
SYSTEM THE ENSEMBLE MEANS ARE STILL THE PREFERRED SOLN FOR THE
FRONT RACING AHEAD INTO THE ALEUTIANS DURING THE WEEKEND. 
OPERATIONAL RUNS ACTUALLY SHOW MORE SPREAD THAN 24 HRS AGO WITH
WAVE/TIMING DETAILS.  AS THE CORE OF THE GRADUALLY WEAKENING BUT
LARGE SCALE WRN PAC SYSTEM REACHES THE ALEUTIANS... THE ECMWF MEAN
RUNS A LITTLE AHEAD OF THE NAEFS MEAN FOR THE SECOND DAY IN A ROW.
 DIFFS REMAIN WELL WITHIN TYPICAL FCST ERRORS AT THAT TIME FRAME
SO A COMPROMISE IS REASONABLE.  THE ONE COMMON THEME IS TO LEAN
AWAY FROM FARTHER NWD SOLNS LIKE THE 06Z GEFS MEAN AND 00Z/06Z GFS
AT SOME FCST HRS.  PREFS FOR SUN-TUE ARE REPRESENTED BY A NEARLY
EVEN BLEND OF THE 00Z NAEFS/ECMWF MEANS.

RAUSCH