Prognostic Meteorological Discussion
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FXAK02 KWNH 131807
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 PM EDT SUN JUL 13 2014

VALID 12Z THU JUL 17 2014 - 12Z MON JUL 21 2014

LATEST GUIDANCE IS CONSISTENT WITH THE GENERAL IDEA OF BROAD
CYCLONIC MEAN FLOW BECOMING ESTABLISHED FROM SIBERIA ACROSS THE
NRN BERING SEA AND MAINLAND ALASKA.  HOWEVER INDIVIDUAL
MODELS/ENSEMBLE MEMBERS REMAIN VARIABLE AND DIVERSE WITH IMPORTANT
SHRTWV DETAILS THAT WILL INFLUENCE THE ULTIMATE STRENGTH AND TRACK
OF A NRN PAC SYSTEM THAT SHOULD BE S OF THE PENINSULA OR ERN
ALEUTIANS AS OF EARLY DAY 4 THU... WITH EFFECTS ON A NRN MAINLAND
FRONTAL BNDRY AS WELL.

FOR THE INITIAL NRN PAC SYSTEM THE ISSUES WITH NRN STREAM SHRTWV
ENERGY LEAD TO POTENTIAL SFC LOW TRACKS ANYWHERE FROM THE NRN
MAINLAND TO NEAR THE SRN PANHANDLE ALONG WITH CONSIDERABLE TIMING
SPREAD.  OVER THE PAST 24 HRS THE GEFS/ECMWF MEANS HAVE GENERALLY
DISPLAYED A DEEPER TREND WITH THE MID LVL TROUGH DEVELOPING NEAR
170W DURING THE FIRST HALF OF THE PERIOD... IN CONTRAST TO SOME
WEAKER TRENDS OVER THE PRIOR DAY OR SO.  ON AVERAGE THE LATEST
TRENDS HAVE LED TO FASTER EJECTION OF THE NRN PAC SYSTEM.  THE
OPERATIONAL ECMWF ALSO SHOWS THIS FASTER TREND SINCE YDAY.  AT THE
MOMENT THE 06Z-12Z GFS ARE AT THE FAST EXTREME WHILE THE 00Z
CMC/UKMET ARE SLOWEST.  BY DAYS 5-6 FRI-SAT MORE AMPLIFIED NRN
STREAM FLOW IN THE 00Z CMC AND TO A LESSER EXTENT 00Z ECMWF LEAD
TO A WELL INLAND TRACK AFTER 12Z FRI IN CONTRAST TO GFS RUNS THAT
ARE MUCH FARTHER S.  SEPARATE NWRN CANADA SFC DEVELOPMENT LEADS TO
CONVERGENCE OF 00Z GFS/ECMWF SOLNS BY SAT THOUGH.  OF PARTICULAR
NOTE IN THE 00Z ECMWF... DEPTH OF ENERGY REACHING THE SERN BERING
SEA INTO THE NERN PAC MID-LATE PERIOD BECOMES MORE EXTREME THAN
ALL BUT A FEW 00Z ENSEMBLE MEMBERS LATE SAT ONWARD.  HIGH SPREAD
AND INDICATIONS OF SOME TREND OSCILLATION ON THE MULTI-DAY TIME
FRAME FAVOR STAYING CLOSER TO THE MIDDLE OF THE SOLN SPREAD BEST
REPRESENTED BY AN AVERAGE OF THE 00Z ECMWF/GFS AND NAEFS/ECMWF
MEANS.

FARTHER UPSTREAM ENERGY IS STILL EXPECTED TO DIG INTO THE WRN SIDE
OF THE OVERALL MEAN TROUGH.  EXACT EVOLUTION OF THIS ENERGY WILL
DETERMINE THE AMPLITUDE/TIMING OF THE LEADING SHRTWV APPROACHING
THE NWRN MAINLAND LATE THIS WEEK AND SFC FRONT DETAILS ACROSS THE
NRN/WRN MAINLAND.  THE 00Z-06Z GFS/00Z ECMWF ACTUALLY COMPARE
DECENTLY TO EACH OTHER AND THE ENSEMBLE MEANS BY DAY 8 MON THOUGH
THEY HAVE DIFFERENT WAYS OF GETTING THERE.  PREFER TO EMPHASIZE
THE ENSEMBLE MEANS TO CAPTURE THE LARGE SCALE AGREEMENT WHILE
AWAITING FOR BETTER DETAIL CLUSTERING AT ANY PARTICULAR POINT IN
TIME LEADING UP TO DAY 8.

GFS RUNS ARE SOMEWHAT STRONGER THAN MOST OTHER SOLNS WITH RESIDUAL
N-CNTRL PAC ENERGY WHOSE CORE MAY RETROGRADE EARLY AND THEN RETURN
EWD JUST S OF THE ALEUTIANS... AND THUS STRONGER WITH THE ASSOC
SFC REFLECTION.  THE 00Z ECMWF IS NEXT CLOSEST BUT KEEPS THE SFC
SYSTEM FARTHER S.  FOR NOW PREFER THE ENSEMBLE MEANS THAT SHOW
HIGHER SFC PRESSURES S OF THE ALEUTIANS.

THE PREFERRED BLEND OF THE 00Z ECMWF/GFS AND NAEFS/ECMWF MEANS FOR
ABOUT THE FIRST HALF OF THE PERIOD REDUCES ECMWF WEIGHTING LATE
FRI/EARLY SAT BEFORE REMOVAL LATE SAT ONWARD... WHILE A 70/30
BLEND OF THE 00Z ECMWF MEAN/NAEFS MEAN IS FAVORED FOR DAYS 7-8
SUN-MON.

RAUSCH

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