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FXAK02 KWNH 031850
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT THU SEP 03 2015

VALID 12Z MON SEP 07 2015 - 12Z FRI SEP 11 2015

THE EXTRATROPICAL EVOLUTION OF HURRICANE IGNACIO CONTINUES TO
OFFER A SIGNIFICANT FCST UNCERTAINTY DURING THE MEDIUM RANGE
PERIOD... WITH RECENT MODEL RUNS DISPLAYING WIDE SPREAD FOR TIMING
AS WELL AS NWD EXTENT OF THE TRACK.  THIS LEADS TO LOWER THAN
DESIRED CONFIDENCE FOR SENSIBLE WEATHER IMPACTS ESPECIALLY OVER
THE ALASKA PANHANDLE.  OFFICIAL TRACK IN THE 1500 UTC CPHC
ADVISORY REPRESENTS AN INTERMEDIATE TIMING AMONG RECENT SOLNS AND
IS MOST CLOSELY APPROXIMATED BY THE 00Z UKMET AND 12Z GFS.  THE
NEW 12Z ECMWF IS MUCH CLOSER TO THIS IDEA THAN THE SLOW 00Z SOLN.
THIS FCST LEADS TO A FARTHER SWD TRACK THAN YDAYS CONTINUITY AND
SHOULD CONFINE POTENTIAL FOR ENHANCED WINDS/RNFL MORE TO THE SRN
PANHANDLE.

FLOW ALONG AND N OF THE NRN PAC WILL CARRY ALONG A SERIES OF
SYSTEMS.  FASTER TREND OF THE 12Z GFS BRINGS IT INTO BETTER
AGREEMENT WITH ECMWF RUNS FOR A LEADING FEATURE REACHING THE
EXTREME NERN PAC AS OF 12Z DAY 4 MON.  FARTHER UPSTREAM THERE IS
IMPROVED CLUSTERING FOR THE SYSTEM FCST TO BE OVER THE WRN BERING
SEA AT THAT TIME.  THIS SYSTEM IS EXPECTED TO LOSE DEFINITION
FAIRLY QUICKLY THOUGH SOME HINT OF LINGERING ENERGY SHEARS EWD
INTO A MODEST SFC LOW NEAR THE SRN COAST MAINLAND.  THE LAST
SYSTEM OF THE SERIES SHOULD TRACK INTO THE WRN ALEUTIANS/BERING
SEA AROUND TUE AND THEN HEAD TOWARD THE SERN BERING SEA/SWRN
MAINLAND.  00Z ECMWF/06Z GEFS/00Z CMC ENSEMBLE MEANS OFFER DECENT
CLUSTERING FOR TRACK THOUGH EXHIBIT MODERATE TIMING DIFFS WHICH
ARE STILL MUCH LESS EXTREME THAN OPERATIONAL MODEL DIFFS.

MAINLAND TROUGHING ALOFT SHOULD PUSH A SFC FRONT SWD OVER THE
MAINLAND EARLY IN THE PERIOD WITH THE FRONT LIKELY SETTLING OVER
THE SRN HALF OF THE MAINLAND THROUGH MID-LATE WEEK.  FROM TUE
ONWARD THE 12Z GFS IS DEEPER THAN MOST OTHER SOLNS WITH THE TROUGH
ALOFT.  OVERALL THE ENSEMBLE MEANS PROVIDE A MORE CONSERVATIVE AND
STABLE FCST FOR THE MAINLAND TROUGH.

DAYS 4-5 MON-TUE INCORPORATE ABOUT 2/3 TOTAL OF THE 00Z UKMET/12Z
GFS TO REFLECT THE FCST FOR EXTRATROPICAL IGNACIO WITH THE REST
CONSISTING OF THE 00Z ECMWF/06Z GEFS MEANS.  HOWEVER 12Z GFS
WEIGHTING IS SUFFICIENTLY LOW NOT TO HAVE AN ADVERSE IMPACT ON
PREFERRED SOLNS OVER MOST OTHER AREAS.  THEN DAYS 6-8 WED-FRI
ADJUST TO ABOUT 2/3 00Z ECMWF MEAN AND 1/3 06Z GEFS MEAN WITH THE
EC MEAN PROVIDING A BETTER DEFINED SRN BERING SEA SYSTEM.

RAUSCH

$$





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