ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 426 PM EDT WED SEP 06 2017 VALID 12Z SUN SEP 10 2017 - 12Z THU SEP 14 2017 A COMPLEX FORECAST REMAINS AHEAD WITH A NUMBER OF SYSTEMS STILL PLAGUED BY MODEL INCONSISTENCIES ALTHOUGH THE FORECAST HAS IMPROVED A BIT FROM YESTERDAY. TO COMMENCE THE PERIOD ON SUNDAY/SEPTEMBER 10...A PRONOUNCED LONGWAVE TROUGH WITH EMBEDDED PERTURBATIONS WILL PUSH THROUGH THE NORTHEASTERN PACIFIC. WHILE MANY SOLUTIONS CAME OUT FLATTER LEADING TO A MORE SUBDUED SURFACE PATTERN...THE 00Z ECMWF WAS QUITE AGGRESSIVE LATE SUNDAY/EARLY MONDAY LOWERING PRESSURES TO 982-MB BY 11/1200Z. EVENTUALLY THIS SHORTWAVE WILL WORK ITS WAY INTO WESTERN CANADA ON MONDAY AFTERNOON WHILE THE NEXT SYSTEM TAKES SHAPE WEST OF THE BERING SEA. AS PART OF AN EXTRATROPICAL TRANSITION FROM WHAT IS CURRENTLY TROPICAL DEPRESSION 19W...GUCHOL...A LONGWAVE TROUGH WILL BE A KEY PLAYER IN THE UPCOMING SYNOPTIC-SCALE PATTERN. MULTI-DAY MODEL OPERATIONAL/ENSEMBLE GUIDANCE COMPARISONS SHOW THE ECMWF SOLUTIONS REMAIN AHEAD OF THE PACK. THIS DISCREPANCY BETWEEN THE GFS/ECMWF CAMPS HAS CONTINUED TO PLAGUE THE FORECAST IN RECENT DAYS AS NEITHER HAS BUDGED MUCH TOWARD THE OTHER. MANY OF THE OPERATIONAL RUNS FAVOR A WELL DEVELOPED SURFACE CYCLONE WHICH THE 00Z ECMWF ENSEMBLE MEAN HAS GENERALLY WASHED OUT. THIS IS LIKELY DUE TO THE VAST SPREAD AMONG ITS 50 MEMBERS. ON THE CONTRARY...THE 06Z/00Z GEFS MEAN SOLUTIONS SHOW MORE PRONOUNCED SURFACE GRADIENTS WHICH SUGGESTS A BETTER CONSOLIDATION AMONG ITS INDIVIDUAL MEMBERS. ACROSS THE NORTHERN EXTENT OF MAP INTO THE ARCTIC OCEAN AND NORTHERN AK...MODELS HAVE COME INTO BETTER AGREEMENT WITH A COMPACT SHORTWAVE DIVING SOUTHWARD LATE SUNDAY/EARLY MONDAY. MANY OF THE RECENT SOLUTIONS DO NOT SHOW AS MUCH SOUTHWARD PROGRESSION AS IT BECOMES UNDERCUT BY THE AFOREMENTIONED SYSTEM TRACKING THROUGH THE BERING SEA. FOR THE DAY 4/5 PERIOD...KEPT DECREASING AMOUNTS OF THE 12Z GFS/00Z ECMWF IN THE MIX IN CONJUNCTION WITH THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS. WEIGHTED THE 00Z ECMWF LESS SIGNIFICANTLY GIVEN THE ROBUST NATURE OF ITS CIRCULATION IN THE GULF OF AK ON DAY 5/MONDAY. EVENTUALLY SHIFTED TOWARD AN ENSEMBLE MEANS APPROACH GIVEN BUILDING UNCERTAINTIES ACROSS THE ENTIRE MAP DOMAIN. GIVEN THE NECESSITY TO DEPICT A MORE DEVELOPED SYSTEM EJECTING OUT OF THE BERING SEA...DEDICATED 70 PERCENT OF THE FORECAST TO THE 06Z GEFS MEAN RELATIVE TO THE 00Z ECMWF ENSEMBLE MEAN. GIVEN THE PERSISTENCE OF SHORTWAVES PUSHING THROUGH MUCH OF THE REGION...THE FORECAST PERIOD WILL FEATURE MORE ABUNDANT CLOUD COVER AND INCREASING PRECIPITATION CHANCES. HIGH TEMPERATURES ACROSS A MAJORITY OF THE STATE WILL BE IN THE 50S EXCEPT FOR THE NORTHERN EXTENT AS READINGS STAY AROUND THE 40 TO 45 DEGREE MARK. THE WETTEST CONDITIONS SHOULD BE ALONG THE SOUTHERN EXTENT OF AK GIVEN THE ACTIVE STORM TRACK. THE BEST ONSHORE FLOW WILL BE ACROSS THE AK PANHANDLE WHERE SOME OF THE HIGHER RAINFALL AMOUNTS ARE LIKELY. RUBIN-OSTER