ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 338 PM EDT THU SEP 14 2017 VALID 12Z MON SEP 18 2017 - 12Z FRI SEP 22 2017 MEDIUM RANGE PERIOD NEXT WEEK WILL FEATURE A SOMEWHAT COMPLICATED NORTHER/SOUTHERN STREAM DANCE AS UPPER RIDGING BUILDS EASTWARD ALONG 45N AND UPPER TROUGHING WEAKENS NORTHWEST OF THE BERING STRAIT. FARTHER UPSTREAM, THE EXTRATROPICAL TRANSITION AND EVENTUAL PATH OF TYPHOON TALIM WILL ALSO COMPLICATE THE PATTERN AS THE MODELS/ENSEMBLES DIVERGE ON ITS TRACK AFTER AROUND TUESDAY. THOUGH BOTH THE GFS AND ECMWF LACK IDEAL CONSISTENCY, THE ECMWF HAS BEEN LESS INCONSISTENT THAN THE GFS, AND THUS WAS THE PREFERRED DETERMINISTIC MODEL THROUGH NEXT WEEK. TO START, THE GFS/UKMET/CANADIAN CLUSTERED CLOSELY ENOUGH TO USE A BLEND OF THEIR SOLUTIONS WITH AN INCREASE IN THE ENSEMBLE MEANS THEREAFTER. THE 12Z GFS APPEARED TOO QUICK TO SLIDE A SFC WAVE EASTWARD LATE MON INTO TUE THROUGH THE GULF OF ALASKA ALONG THE WARM FRONT COMPARED TO THE OTHER MODELS AND ALSO APPEARED TOO FAR SOUTH WITH THE BOUNDARY (NEAR 50N) BACK TOWARD THE PARENT LOW. THOUGH THE ECMWF MAY HAVE BEEN TOO FAR NORTH WITH THAT BOUNDARY, THE BLEND OF THE OTHER MODELS MAINTAINED CONTINUITY FROM YESTERDAY NEAR OR JUST SOUTH OF THE ALEUTIANS. THEREAFTER, FOR WED-THU, KEPT THE IDEA OF A SLOWLY MOVING SYSTEM EASTWARD INTO AND THE GULF OF ALASKA WITH A WEAKENING NORTHERN STREAM SYSTEM IN THE BERING SEA. FARTHER UPSTREAM, MODELS DIVERGED IN HOW TO HANDLE THE EXTRATROPICAL TRANSITION OF TYPHOON TALIM AS IT EITHER CONTINUES NORTHWARD THROUGH THE SEA OF OKHOTSK (GFS) OR TURNS EASTWARD ACROSS SOUTHERN KAMCHATKA (ECMWF/UKMET/CANADIAN). OPTED TO BELIEVE THE BIGGER CLUSTER OF SOLUTIONS INCLUDING THE ECMWF THAT ALLOW IT TO SLIDE EASTWARD (SYSTEM SEEN SOUTH OF THE WESTERN ALEUTIANS NEXT THU/FRI). SINCE THE ECMWF ENSEMBLES GENERALLY HANDLE AMPLIFIED FLOW BETTER THAN THE GEFS MEMBERS, GAVE MUCH MORE WEIGHTING TO THAT ENSEMBLE SYSTEM BY NEXT WED-FRI, WITH LESS WEIGHTING TO THE GEFS AND ECMWF DETERMINISTIC. THIS WOULD TAKE THE LEAD SYSTEM TOWARD THE PANHANDLE BY NEXT FRIDAY AS THE UPPER PATTERN MAY FLATTEN OUT. FRACASSO