ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 PM EDT WED APR 05 2017 VALID 12Z SUN APR 09 2017 - 12Z THU APR 13 2017 TODAY'S FCST CONTINUED TO RELY ON OPERATIONAL MODEL GUIDANCE TO THE BEST POSSIBLE EXTENT GIVEN REASONABLE DEFINITION OF TWO PROMINENT ALEUTIAN SYSTEMS. THE FIRST SYSTEM SHOULD BE JUST S OF THE ISLANDS AT THE START OF THE PERIOD EARLY DAY 4 SUN AND THEN TRACK E-SE INTO THE ERN PACIFIC BEFORE PSBLY CURVING FAR ENOUGH NWD FOR ITS NRN PERIPHERY TO BEGIN HAVING SOME INFLUENCE ON THE SRN PANHANDLE AT THE END OF THE PERIOD. AS OF SUN-MON THE CONSENSUS TRACK IS A TAD N OF WHAT IT WAS 24 HRS AGO. THE NEXT SYSTEM, MOST LIKELY TO TRACK INTO THE WRN ALEUTIANS AND THE SRN BERING SEA, HAS HAD A HISTORY OF WIDE MODEL/ENSEMBLE SPREAD AND SIGNIFICANT RUN TO RUN CONTINUITY CHANGES. COMPARED TO THE PAST DAY OR SO THE GUIDANCE CLUSTERING HAS IMPROVED SOMEWHAT INTO DAYS 6-7 TUE-WED BUT GFS RUNS IN PARTICULAR STILL DIVERGE CONSIDERABLY AFTER THAT TIME. OVER THE PAST 2-3 DAYS THE ECMWF ENSEMBLE MEAN HAS BEEN THE TRENDSETTER FOR THIS SYSTEM'S TRACK, WITH RECENT DEEPER TRENDS FAVORING AN AVERAGE AMONG THE STRONGER OPERATIONAL GUIDANCE. THE LATEST ECMWF MEAN TREND HAS BEEN TO DELAY WEAKENING/EWD SHEARING BY DAYS 7-8 WED-THU THUS ADDING SUPPORT FOR MAINTAINING SOME 00Z ECMWF/CMC COMPONENT TO THE FCST THROUGH THE END OF THE PERIOD. THE 12Z GFS WAS CLOSE ENOUGH TO ALLOW FOR MINORITY INCLUSION ALONG WITH THE 00Z ECMWF AND CMC INTO EARLY WED. THE FCST IS MORE NEBULOUS ACROSS THE MAINLAND AND NERN PAC WITH MULTIPLE SMALLER SCALE DETAIL ISSUES THAT TEND TO HAVE LOW PREDICTABILITY IN THE EXTENDED TIME FRAME. THE MOST COMMON THEMES ARE A GENERAL WEAKNESS ALOFT OVER THE NERN PAC/GULF OF ALASKA WHILE ABOVE NORMAL HGTS PREVAIL OVER THE MAINLAND. TELECONNECTIONS RELATIVE TO A CORE OF NEGATIVE HGT ANOMALIES OVER THE ERN PAC STILL SUGGEST THAT WRN CANADA MEAN RIDGING COULD EXTEND INTO THE MAINLAND TO SOME DEGREE AS ENSEMBLE MEANS HAVE TENDED TO SHOW. HOWEVER SOME INDIVIDUAL MODEL SOLNS SHOW POTENTIAL FOR A MODEST WEAKNESS SOMEWHERE OVER THE MAINLAND BTWN THE WRN CANADA RIDGE AND A RIDGE THAT MAY BUILD OVER ERN SIBERIA LATE IN THE PERIOD. AT THE MOMENT THERE IS MINIMAL SUPPORT FOR THE LATE PERIOD FULL-LATITUDE RIDGE DEPICTED AT DIFFERING LONGITUDES IN THE 12Z AND 06Z GFS RUNS, OR THE EARLY WEEK SMALLER SCALE RIDGE OVER THE SRN MAINLAND IN THE 00Z/06Z GFS RUNS. PREFERENCE FOR SOME ENSEMBLE MEAN INPUT BY DAYS 6-8 TUE-THU LED TO INTRODUCING 30-50 PCT ENSEMBLE MEAN WEIGHTING FOR THAT TIME FRAME WITH SOMEWHAT MORE 00Z ECMWF MEAN THAN 06Z GEFS MEAN. THE RESULTING BLEND DOWNPLAYED LOW CONFIDENCE DETAILS IN THE OPERATIONAL COMPONENTS. EVEN WITH THE DETAIL DIFFS ALOFT THERE IS BETTER AGREEMENT AT THE SFC DAYS 7-8 WITH A STRENGTHENING MAINLAND GRADIENT BTWN ARCTIC/NWRN CANADA HIGH PRESSURE AND THE OVERALL AXIS OF LOWER PRESSURES ACROSS THE BERING/NERN PAC. RAUSCH