ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 246 PM EDT SUN JUN 25 2017 VALID 12Z THU JUN 29 2017 - 12Z MON JUL 03 2017 TODAY'S FCST SHOWS DECENT CONTINUITY/CONSENSUS FOR THE LARGE SCALE PATTERN EVOLUTION WHILE REFINING NERN PACIFIC/GULF OF ALASKA DETAILS TO REFLECT IMPROVING CLUSTERING OF GUIDANCE. CONTINUE TO EXPECT HGT FALLS TO PROCEED INTO THE EXTREME NERN PAC/GULF OF ALASKA WITH THE ARRIVAL OF LEADING ENERGY NEAR THE START OF THE PERIOD AND THEN THE EWD PROGRESSION OF UPSTREAM ENERGY FROM THE ALEUTIANS AND VICINITY. BY NEXT SAT-MON THIS SHOULD LEAD TO A CLOSED LOW ALOFT ALONG OR JUST S OF A PATH BTWN KODIAK ISLAND AND THE SRN PANHANDLE. MEANWHILE WRN CANADA MEAN RIDGING SHOULD BUILD A RIDGE AXIS STEADILY MORE WWD ACROSS THE MAINLAND. SOME GUIDANCE HAS BEEN SHOWING POTENTIAL FOR AN UPR HIGH TO CLOSE OFF OVER OR NEAR THE CNTRL-NERN MAINLAND/NRN YUKON BY LATE IN THE PERIOD. IN THIS LATER TIME FRAME RECENT GFS RUNS HAVE GENERALLY BEEN A LITTLE CLOSER TO AN AVG OF THE ENSEMBLE MEANS FOR THE UPR RIDGE/HIGH POSN THAN THE 00Z ECMWF THAT IS FARTHER SW. GUIDANCE SPREAD HAS NARROWED FOR WHAT HAS BEEN A DIFFICULT FCST FOR ONE OR MORE CNTRL PAC INTO NERN PAC/GULF OF ALASKA WAVES, BUT PLENTY OF UNCERTAINTY REMAINS. CURRENT MAJORITY SCENARIO HAS A LEADING SYSTEM THAT IS SOMEWHAT SLOWER THAN YDAY'S FAST GFS/UKMET SOLNS, FOLLOWED BY ANOTHER WAVE (SUPPORTED BY AN UPR LOW NOW N OF JAPAN) AND THEN ALEUTIANS ENERGY THAT MERGE WITH/MAINTAIN THE LEADING SYSTEM. THE END RESULT IS LOW PRESSURE THAT SHOULD DRIFT TOWARD KODIAK ISLAND, WITH MODELS/MEANS KEEPING THE FEATURE WELL DEFINED FOR A LONGER TIME THAN PREVIOUS FCST. THERE ARE STILL OTHER SOLNS THAT KEEP FEATURES MORE SEPARATE OR INVOLVE DIFFERING INTERACTION. FROM DAY 4 THU INTO DAY 5 FRI THE 06Z GFS/00Z ECMWF PROVIDED THE BEST TEMPLATE WITH SUPPORT IN PRINCIPLE FROM THE ENSEMBLE MEANS. THEN THE 00Z ECMWF BECAME MORE PROGRESSIVE THAN THE MEANS AND 00Z-06Z GFS/00Z CMC RUNS. THUS BY SAT PREFERRED TO REDUCE ECMWF WEIGHT MORE QUICKLY THAN THE 06Z GFS WHILE INCREASING 06Z GEFS/00Z ECMWF MEAN INPUT. AMONG NEW 12Z GUIDANCE THERE IS STILL A DECENT RANGE OF SOLNS FOR PROGRESSION/DETAILS. THERE IS A HINT OF FASTER TIMING IN GUIDANCE AS A WHOLE OVER THE PAST DAY BY THE LATTER HALF OF THE PERIOD BUT THE FACT THAT AN UPR HIGH MAY CLOSE OFF TO THE N SEEMED TO FAVOR STICKING WITH AN AVG OF THE MEANS FOR THE TIME BEING. UPSTREAM THERE IS STILL FAIR AGREEMENT ON THE DEVELOPMENT OF A MEAN TROUGH FROM SIBERIA SWD THROUGH THE EXTREME WRN BERING SEA AND WRN PAC. HOWEVER BY MID-LATE PERIOD THERE IS WIDE MODEL/ENSEMBLE SPREAD AND POOR RUN-RUN MODEL CONTINUITY FOR DETAILS WITHIN AND AHEAD OF THE MEAN TROUGH, ULTIMATELY AFFECTING THE FCST ACROSS MUCH OF THE ALEUTIANS/BERING SEA. FOR NOW IT IS DIFFICULT TO HAVE ANY CONFIDENCE IN A PARTICULAR MODEL SOLN SO PREFER TO LEAN MORE TO THE ENSEMBLE MEANS WHILE AWAITING A BETTER CONSENSUS. BASED ON ABOVE FCST CONSIDERATIONS OVER THE COURSE OF THE PERIOD, TODAY'S STARTING BLEND CONSISTED OF THE 06Z GFS/00Z ECMWF INTO DAY 5 FRI FOLLOWED BY GRADUALLY DECREASED OPERATIONAL RUN/INCREASED ENSEMBLE MEAN WEIGHTING SUCH THAT DAY 8 MON USED THE MEANS EXCLUSIVELY. RAUSCH