Prognostic Meteorological Discussion
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FXAK02 KWNH 021855
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT SUN AUG 02 2015

VALID 12Z THU AUG 06 2015 - 12Z MON AUG 10 2015

ENSEMBLE MEANS HAVE BEEN SHOWING AN EVOLUTION TOWARD A LARGE SCALE
MEAN TROUGH WITH AN AXIS JUST W OF THE MAINLAND BY THE END OF THE
PERIOD... BY WAY OF AN AMPLIFYING NRN STREAM TROUGH TO THE NW OF
THE MAINLAND AND EVENTUAL PSBL INCORPORATION OF A SYSTEM TRACKING
NEWD FROM THE WRN PAC.  COMBINED UNCERTAINTIES WITH EACH FEATURE
AND TYPICAL FCST ERROR 6-8 DAYS OUT IN TIME TEMPER CONFIDENCE IN A
SPECIFIC SOLN AT THIS TIME.  HOWEVER WITH THAT BEING SAID... THERE
IS ENOUGH SIMILARITY AMONG THE 00Z ECMWF/06Z GFS AND THEIR
RESPECTIVE ENSEMBLE MEANS PLUS OPERATIONAL MODEL SIGNALS TO FAVOR
A COMPROMISE BTWN MODEL AND ENSMEAN IDEAS.  THIS BLEND IS ALSO
REASONABLE DOWNSTREAM WHERE DIFFS EXIST OVER THE MAINLAND/NERN PAC.

WITH THE TROUGH AMPLIFYING NW OF THE MAINLAND THE PRIMARY MODEL
SIGNAL IS TOWARD A DEEPER EMBEDDED UPR LOW RELATIVE TO WHAT THE
MEANS HAVE INDICATED THUS FAR.  INDIVIDUAL MODEL RUNS HAVE NOT YET
STABILIZED ENOUGH TO PROVIDE ENTHUSIASTIC ENDORSEMENT OF A
SPECIFIC RUN BUT WITH THE 00Z GFS LEANING TO THE SLOW SIDE OF MOST
GUIDANCE... THE 00Z ECMWF/06Z GFS PROVIDE A MORE PALATABLE
OPERATIONAL COMPONENT TO THE BLEND.  MEANWHILE RECENTLY STRONGER
ENSEMBLE MEAN TRENDS FOR THE WRN PAC/BERING SEA SYSTEM SEEM TO BE
POINTING TOWARD OPERATIONAL RUNS THAT ARE DEEPER THAN THE MEANS.
AT MOST FCST HRS THE 00Z GFS IS ON THE FASTER SIDE... AGAIN
FAVORING THE 00Z ECMWF/06Z GFS AS OPERATIONAL COMPONENTS.  NOT
SURPRISINGLY THE MEANS DEPICT A SOMEWHAT MORE PHASED OVERALL
TROUGH ALOFT BY DAY 8 MON BUT GIVEN THE TIME FRAME THOSE TWO MODEL
RUNS ARE REMARKABLY CLOSE TO THE MEANS FOR THE SFC LOW TRACK.

AHEAD OF THIS EVOLUTION... THERE ARE ONGOING DETAIL UNCERTAINTIES
OVER THE MAINLAND AND NERN PAC.  THUS FAR GUIDANCE HAS BEEN
UNDECIDED OVER WHAT PROPORTION OF TROUGH ENERGY OVER THE MAINLAND
AS OF DAY 4 THU WILL DROP INTO THE EXTREME NERN PAC VERSUS THE
REST THAT EJECTS EWD.  THIS TYPE OF EVOLUTION CAN BE DIFFICULT TO
RESOLVE BEYOND THE SHORT RANGE.  GFS/ECMWF RUNS HAVE BEEN WAFFLING
ON STRENGTH OF MAINLAND/NERN PAC ENERGY AND WHILE SOME INDIVIDUAL
ENSEMBLE MEMBERS ARE AS DEEP OR DEEPER THAN THE STRONGER
OPERATIONAL RUNS LIKE THE 00Z/12Z GFS OR OLD 12Z/01 ECMWF... THERE
ARE ENOUGH WEAKER MEMBERS TO KEEP THE MEANS ON THE MODEST SIDE FOR
DEPTH ALOFT.  THEREFORE PREFER AN INTERMEDIATE SOLN UNTIL BETTER
AGREEMENT EMERGES.  THIS ENERGY WILL HAVE SOME INFLUENCE ON THE
SYSTEM TRACKING ACROSS THE NERN PAC.  TRENDS OVER THE PAST DAY
HAVE BEEN SOMEWHAT FASTER WHILE LATEST OPERATIONAL RUNS TRACK THE
SFC LOW SOMEWHAT SE OF THE ENSMEANS.

RAUSCH

$$





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