Prognostic Meteorological Discussion
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FXAK02 KWNH 011844
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 PM EDT SAT AUG 01 2015

VALID 12Z WED AUG 05 2015 - 12Z SUN AUG 09 2015

FLOW OVER AND W/NW OF THE MAINLAND SHOULD BE CYCLONIC IN THE MEAN.
 WITHIN THIS STREAM THE LATEST GUIDANCE GENERALLY SUGGESTS THAT A
LEADING SHRTWV TROUGH SHOULD AMPLIFY OVER THE MAINLAND AND THEN
EJECT NEWD AS A SOMEWHAT LARGER SCALE TROUGH WITH PSBL EMBEDDED
CLOSED LOW EVOLVES UPSTREAM.  THE BEST CLUSTER OF SOLNS WOULD HAVE
THE AXIS OF THE LATTER TROUGH NEARING THE NWRN MAINLAND NEXT
WEEKEND.  PRIMARY EMPHASIS OVER THIS AREA IS TO LEAN AWAY FROM THE
06Z-12Z GFS/06Z GEFS MEAN.  THE 06Z/12Z GFS AND 00Z UKMET ARE THE
PRONOUNCED DEEPER SOLNS WITH THE LEADING MAINLAND TROUGH/UPR LOW.
THE GFS RUNS ARE ALSO QUITE AGGRESSIVE IN PULLING THIS TROUGH
ENERGY SWD INTO THE NERN PAC.  THE 06Z GEFS MEAN BECOMES OUT OF
PHASE WITH CONSENSUS FOR UPSTREAM FLOW... ULTIMATELY LEADING TO
ISSUES OVER THE MAINLAND/NERN PAC AS WELL.  THUS FAR ECMWF RUNS
HAVE HAD BETTER CONTINUITY WITH THE MAINLAND TROUGH.

THERE HAS BEEN ENOUGH VARIABILITY THUS FAR TO TEMPER CONFIDENCE
FOR THE SYSTEM FCST TO BE JUST S OF THE ERN ALEUTIANS/PENINSULA AS
OF 12Z WED.  HOWEVER AT THE MOMENT THE 00Z GFS/ECMWF OFFER SIMILAR
SOLNS THAT COMPARE FAVORABLY TO THE FULL RANGE OF GUIDANCE.  DUE
IN PART TO AFOREMENTIONED ISSUES TO THE N... THE 06Z GEFS MEAN IS
ON THE WEAK/FAST SIDE WHILE THE 06Z-12Z GFS APPEAR FAST AS WELL.
OPERATIONAL MODEL AGREEMENT TOWARD A BETTER DEFINED SYSTEM
SFC/ALOFT VERSUS THE ENSEMBLE MEANS WOULD FAVOR GREATER WEIGHTING
OF THE 00Z GFS/ECMWF AT LEAST INTO DAY 6 FRI.

A FAIRLY BLOCKY PATTERN FARTHER WWD SHOULD LEAD TO SLOW EVOLUTION
OF A NWRN PAC/ALEUTIANS SYSTEM.  BY NEXT WEEKEND THE 00Z ECMWF
MEAN AND 00Z GFS BECOME A LITTLE FASTER THAN OTHER SOLNS.  BY THIS
TIME PREFER TO LEAN SOMEWHAT TOWARD THE SLOWER MAJORITY CLUSTER...
AND OPERATIONAL ECMWF CONTINUITY... REPRESENTED BY THE 00Z NAEFS
MEAN/ECMWF BUT MAINTAINING SOME INCLUSION OF THE ECMWF MEAN AS ITS
SOLN HAS BEEN FAIRLY STABLE OVER RECENT RUNS AS WELL.  THE EXACT
AMPLITUDE OF THE NRN STREAM TROUGH MAY BEGIN TO PLAY AN IMPORTANT
ROLE IN THE FCST TOWARD THE END OF THE PERIOD.

ABOVE CONSIDERATIONS YIELD AN INITIAL FCST BLEND CONSISTING OF 70
PCT TOTAL 00Z GFS/ECMWF VERSUS THE 00Z NAEFS/ECMWF MEANS DAYS 4-5
WED-THU... INCREASING 00Z NAEFS WEIGHTING AT THE EXPENSE OF THE
00Z GFS OVER THE COURSE OF DAY 6 FRI... THEN USING NEARLY EVEN
AMOUNTS OF THE 00Z ECMWF/ECMWF MEAN/NAEFS MEAN DAYS 7-8 SAT-SUN.

RAUSCH

$$




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