ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 240 PM EDT SAT OCT 01 2016 VALID 12Z WED OCT 05 2016 - 12Z SUN OCT 09 2016 THE AVERAGE OF LATEST GUIDANCE CONTINUES TO SHOW THE ESTABLISHMENT OF A DEEP MEAN LOW ALOFT OVER THE BERING SEA WITH A DOWNSTREAM RIDGE BUILDING OVER THE MAINLAND AND DRIFTING GRADUALLY NEWD WITH TIME. WITHIN/AROUND THIS LARGE SCALE EVOLUTION THERE ARE SIGNIFICANT DIFFS IN THE DETAILS FOR INDIVIDUAL SYSTEMS AND THE SHAPE/POSITION OF THE DOWNSTREAM RIDGE. IN ADDITION THERE IS FAIRLY HIGH SENSITIVITY/UNCERTAINTY IN SOME ASPECTS OF THE NERN PACIFIC FORECAST THAT MAY AFFECT PORTIONS OF THE ALASKA PANHANDLE. TO THE WEST OF THE MAINLAND... THERE IS FAIRLY GOOD AGREEMENT WITH THE LEADING STRONG SFC LOW TRACKING INTO THE BERING SEA BY LATE WED-THU. HOWEVER DIFFS CONTINUE TO BE SIGNIFICANT WITH THE TRAILING SYSTEM THAT IS LIKELY TO BE A COMBINATION OF EXTRATROPICAL TYPHOON CHABA AND MID-LATITUDE ENERGY EMERGING FROM ERN ASIA. AS WAS THE CASE 24 HRS AGO THE 00Z-06Z GFS RUNS TRACK THIS SECOND FEATURE ACROSS THE NRN PAC INSTEAD OF WRAPPING INTO THE MEAN LOW OVER THE BERING SEA AS DEPICTED BY ECMWF/CMC AND GEFS/ECMWF/CMC MEAN RUNS. THE NUMBER OF INDIVIDUAL ENSEMBLE MEMBERS SHOWING THE 00Z-06Z GFS SCENARIO IS FAIRLY LOW. OVERALL PREFERENCE WOULD BE FOR THE MAJORITY CLUSTER OF 00Z ECMWF/CMC AND 00Z GEFS/ECMWF MEAN SOLNS WHICH WOULD MAINTAIN FAIRLY GOOD CONTINUITY. NEW 12Z SOLNS THUS FAR ARE SHOWING MORE HINTS OF A COMPROMISE SCENARIO WITH THE GFS A TAD NWD OF PREVIOUS RUNS AND THE 12Z CMC JUST S OF THE ALEUTIANS UNTIL TRACKING INTO THE SERN CORNER OF THE BERING SEA. THE 12Z GEFS MEAN HAS BEEN PULLED A BIT SWD AS WELL. OVER THE MAINLAND AND NERN PACIFIC... WITH TYPICAL DIFFS IN THE DETAILS THERE ARE INDICATIONS FROM RECENT OPERATIONAL MODEL RUNS THAT STRENGTHENING MAINLAND RIDGING DURING THE FIRST HALF OF THE PERIOD MAY YIELD A CLOSED HIGH AROUND FRI. ANOTHER POSSIBILITY SEEN MORE IN 12Z GFS/GEFS/UKMET RUNS IS PERSISTENCE OF THE INITIAL CLOSED HIGH OVER/NEAR THE NRN MAINLAND. GIVEN FCST UNCERTAINTIES AN OPERATIONAL/ENSEMBLE MEAN COMPROMISE APPEARS BEST FOR THIS PART OF THE FCST. EXACTLY HOW THIS RIDGE EVOLVES MAY HAVE AN INFLUENCE ON EARLY PERIOD GULF OF ALASKA/PANHANDLE ENERGY THAT MAY IN TURN PLAY SOME ROLE IN THE FCST OF A WAVE EXPECTED TO TRACK S OF THE PANHANDLE THU ONWARD. THE 00Z ECMWF IS QUITE WEAK WITH N-CNTRL PAC ENERGY AND THUS VERY SUPPRESSED AT THE SFC. ON THE OTHER HAND 06Z/12Z GFS AND SLOWER 00Z CMC RUNS ARE STRONGEST WITH N-CNTRL PAC ENERGY AND SHOW GREATER INTERACTION LEADING TO A SFC WAVE THAT REACHES UP TO 55N LATITUDE. 00Z/06Z GEFS MEANS ARE ESSENTIALLY A COMPROMISE BTWN THE 06Z GFS AND FARTHER SEWD 00Z RUN. THE ECMWF MEAN IS NOT QUITE AS WEAK/SUPPRESSED AS THE OPERATIONAL RUN AND BY 12Z FRI ENDS UP WITH A PATTERN MORE SIMILAR TO THE CMC/GEFS MEANS. SO WOULD ULTIMATELY TEND TO FAVOR A SOLN CLOSEST TO THE LATEST GEFS MEANS WITH A SFC LOW TRACK NOT REACHING MUCH FARTHER NWD THAN 50N LATITUDE. AT THE START OF THE PERIOD A COMPROMISE BTWN THE 06Z GFS/00Z ECMWF PROVIDED A REASONABLE STARTING POINT FOR WEAKENING LOW PRES THAT MAY BE NEAR THE SRN TIP OF THE PANHANDLE AS OF 12Z WED. 12Z RUNS ARE STILL DIVERSE WITH THE GFS STILL FARTHEST NWD BUT THE CMC TRENDING WELL SWD. BASED ON OVERALL PREFS THE INITIAL BLEND CONSISTS OF THE 00Z ECMWF/06Z GFS ON DAY 4 WED... BEGINS INCORPORATING THE 00Z GEFS/ECMWF MEANS DAY 5 THU... AND THEN GOES WITH THE 00Z ECMWF/ECMWF MEAN/GEFS MEAN CLUSTER THEREAFTER. MINOR EDITING WAS PERFORMED TO ACHIEVE THE DESIRED SOLN OVER THE NERN PAC AROUND THU-FRI. RAUSCH