ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 335 PM EDT SUN SEP 03 2017 VALID 12Z THU SEP 07 2017 - 12Z MON SEP 11 2017 ...THE STORMY PERIOD CONTINUES FOR THE GULF OF AK... THE EXTRATROPICAL TRANSITION OF TS SANVU LEADS TO THE NEXT CYCLONE IN THE LOWER ALEUTIANS WED 06 SEP...CONTINUING SOUTH OF THE MIDDLE ALEUTIANS THU 07 SEP...AND SOUTHEAST OF KODIAK ISLAND BY 12Z FRI 08 SEP...WHERE THE CIRCULATION SLOWS DOWN AND OCCLUDES. THE 06Z-12Z GFS RUN CLUSTERS WITH THE 00Z ECMWF/ECMWF ENSEMBLE MEAN WITH THE LOW TRACK THROUGH THU NIGHT. THE 06Z-12Z GFS PARTS COMPANY WITH THE RESPECTIVE GEFS/ECMWF ENSEMBLE MEANS AND OPERATIONAL RUNS IN MOVING THE LOW MORE QUICKLY SOUTHEAST TOWARDS THE WATERS OFF PRINCE OF WALES ISLAND 12Z SUN 10 SEP. THE 12Z GEFS AND 00Z ECMWF ENSEMBLE MEANS ARE IN BETTER AGREEMENT IN MOVING THE CYCLONE MORE SLOWLY AND PERSISTING IN THE GULF OF AK AND HAVE BETTER CONTINUITY...SO ARE PREFERRED. GUIDANCE CONTINUES TO SHOW A FRONT WITH WAVES OF LOW PRESSURE ACROSS NORTHERN AK/YUKON/ADJACENT COASTAL WATERS...WITH HIGH PRESSURE TO THE NORTH IN THE BEAUFORT SEA IN THE ECMWF/CANADIAN GLOBAL FORCING THE FRONT SOUTH THE LATTER HALF OF THIS WEEK. ADDITIONAL WAVES FORM NORTH OF THE BERING STRAIT IN THE CHUKCHI SEA EARLY NEXT WEEK AND MOVE EAST OR SOUTHEAST. THE 12Z ECMWF WAS FASTER AND STRONG WITH THE LOW NORTH OF THE NORTH SLOPE IN THE SOUTHERN BEAUFORT SEA EARLY NEXT WEEK...WHILE THE 12Z GFS WAS SLOWER LIKE THE 00Z RUN. THE RUN TO RUN AND MODEL TO MODEL DIFFERENCES REMAIN TO BE SOLVED WITH GREATER WEIGHTING ON THE ECMWF ENSEMBLE MEAN THAN ANY ONE RUN USED TO MITIGATE DIFFERENCES. THE MODELS HAVE LARGE DIFFERENCES ON THE NEXT UPPER TROUGH AND SURFACE LOW PRESSURE DEVELOPING OVER THE NORTHERN PACIFIC. THE GFS AND ECMWF SHOW SIGNIFICANT RUN TO RUN DIFFERENCES/DIFFERENCES WITH EACH OTHER/DIFFERENCES BETWEEN THE OPERATIONAL RUNS AND THEIR RESPECTIVE MEANS. THE ENSEMBLE MEANS ARE FAVORED UNTIL BETTER AGREEMENT AND/OR CONTINUITY DEVELOPS. PETERSEN