ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 249 PM EDT MON SEP 26 2016 VALID 12Z FRI SEP 30 2016 - 12Z TUE OCT 04 2016 GUIDANCE CONTINUES TO SHOW DIFFERENCES IN HOW MID LVL ENERGY AND ASSOC SFC SYSTEM INITIALLY NEAR THE ALEUTIANS INTERACTS WITH A MEAN UPR LOW OVER/NEAR SIBERIA... WITH FURTHER QUESTION MARKS ON HOW DOWNSTREAM MAINLAND RIDGING EVOLVES WITH TIME. INDIVIDUAL MODELS/ENSEMBLE MEMBERS DISPLAY A FAIR AMOUNT OF SPREAD WITH THE ULTIMATE TRACK OF ALEUTIANS/BERING SEA LOW PRESSURE DURING THE FIRST HALF OF THE PERIOD. OVER THE PAST COUPLE DAYS OPERATIONAL RUNS HAVE APPEARED TO BE WELL AHEAD OF THE ENSEMBLE MEANS IN DEPICTING THE STRENGTH OF THIS FEATURE AS ENSEMBLE MEMBER SPREAD HAS BEEN DILUTING THE RESULTING MEANS. AT LEAST THE LATEST RUNS OF THE MEANS ARE TRENDING TOWARD BETTER DEFINITION AND OFFER REASONABLE SUPPORT FOR STARTING WITH A 00Z GFS/ECMWF BLEND FOR TRACK FROM DAY 4 FRI INTO DAY 5 SAT. AS THE ALEUTIANS/BERING SEA SYSTEM HEADS INTO THE MAINLAND RIDGE MOST GUIDANCE EXPECTS A SPLITTING OF ENERGY/MSTR WITH SOME LIFTING BACK NWWD TOWARD THE MEAN UPR LOW OVER/NEAR SIBERIA AND THE REST BEING STRUNG OUT ACROSS THE SWRN COAST OF THE MAINLAND/ALASKA PENINSULA AND INTO NERN PAC/GULF OF ALASKA. THE 06Z GFS BRINGS MORE MID LVL ENERGY/MSTR INTO AND ACROSS THE MAINLAND AND IS NOT FAVORED GIVEN THE EXPECTED STRENGTH OF THE DOWNSTREAM RIDGE. THE 12Z GFS HAS ADJUSTED SOMEWHAT AWAY FROM THE 06Z RUN. MOST OPERATIONAL MODEL RUNS OVER THE PAST COUPLE DAYS HAVE BEEN SIGNALING AN UPR HIGH CLOSING OFF OVER THE MAINLAND AROUND SAT WITH INCREASINGLY VARIED SOLNS ON THE PATH OF THIS HIGH LATER IN THE PERIOD. UP UNTIL THE PAST 1-2 RUNS THE GEFS MEANS HAVE BEEN AHEAD OF THE ECMWF MEAN IN HINTING AT OPERATIONAL SIGNALS THAT THE RIDGE WOULD CLOSE OFF. NOW THE 00Z ECMWF MEAN HOLDS ONTO A STRONGER-NWD RIDGE/HIGH THAN THE 06Z GEFS MEAN THOUGH THE 00Z GEFS MEAN WAS CLOSER TO THE ECMWF MEAN. THUS AFTER A MODEL/ENSEMBLE MEAN TRANSITION LATE SAT INTO SUN... PREFS LEAN TOWARD MAJORITY WEIGHTING OF THE 00Z ECMWF MEAN RELATIVE TO THE 00Z GEFS/NAEFS MEANS. GUIDANCE TENDS TO HAVE DIFFICULTY IN FORECASTING THE PATH OF CLOSED HIGHS VERY FAR INTO THE FUTURE SO CONFIDENCE DECLINES RAPIDLY AFTER SAT-SUN. ELSEWHERE... THERE IS REASONABLE AGREEMENT THAT SHRTWV ENERGY DIVING DOWN THE ERN SIDE OF THE MAINLAND RIDGE WILL PASS OVER THE PANHANDLE NEAR THE START OF THE PERIOD FOLLOWED BY A GENERAL WEAKNESS WITH LOW CONFIDENCE ON DETAILS. MEANWHILE PROGRESSIVE FLOW FROM ASIA ACROSS THE NRN PAC/ALEUTIANS/BERING SEA MAY CARRY ONE OR MORE WEAK FEATURES MID-LATE PERIOD... AGAIN WITH FAIRLY LOW CONFIDENCE GIVEN FEATURE SCALE AND FAST FLOW. IN BOTH CASES THE PREFERRED INCREASING EMPHASIS ON ENSEMBLES WITH TIME PROVIDES A GOOD CONSERVATIVE STARTING POINT WHILE AWAITING BETTER AGREEMENT FOR SPECIFICS. RAUSCH