ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 255 PM EDT SAT MAY 27 2017 VALID 12Z WED MAY 31 2017 - 12Z SUN JUN 04 2017 THERE IS REASONABLE AGREEMENT ON THE LARGE SCALE PATTERN AT LEAST FROM THE PERSPECTIVE OF RECENT ENSEMBLE MEANS, WITH AN AXIS OF RELATIVELY LOWER HGTS ALOFT (CONTAINING ONE OR MORE EMBEDDED UPR LOWS) FROM THE ALEUTIANS/BERING SEA INTO NERN PACIFIC WHILE CANADIAN RIDGING EXTENDS OVER A SIGNIFICANT PORTION OF MAINLAND ALASKA. HOWEVER THE FULL SPECTRUM OF INDIVIDUAL ENSEMBLE MEMBERS AND OPERATIONAL MODEL RUNS UP TO THIS POINT WOULD SUGGEST CONSIDERABLE UNCERTAINTY WITH SPECIFICS ACROSS MUCH OF THE NRN PAC/ALEUTIANS INTO BERING SEA WITH GUIDANCE SPREAD EXTENDING INTO THE MAINLAND AND PANHANDLE AS WELL. AS OF DAY 4 WED THERE IS DECENT MODEL AGREEMENT ON A CNTRL ALEUTIANS SYSTEM FOR WHICH THE 06Z GEFS IS THE ONLY ENSEMBLE MEAN THAT HAS SIMILAR DEFINITION. MEANWHILE THERE IS ALREADY A MODERATE AMOUNT OF SPREAD FOR THE SYSTEM TO THE S/SE OF KODIAK ISLAND. FOR THIS EARLY PART OF THE FCST AN OPERATIONAL MODEL BLEND, MORE 12Z GFS/00Z ECMWF RELATIVE TO UKMET/CMC RUNS, REFLECTED CONSENSUS IDEAS WHILE RESOLVING POSN DIFFS FOR THESE SYSTEMS. NOTE THAT 00Z ECMWF WEIGHTING WAS KEPT LOW ENOUGH TO LEAN AWAY FROM ITS FARTHER NWD SYSTEM OFF KODIAK ISLAND, WITH A SWD TREND OF THE GFS FROM 00Z TO 06Z THEN 12Z RUNS REINFORCING THE MORE SRN CLUSTER. THIS SOLN ALSO PROVIDED CONSENSUS DETAIL AND INTERMEDIATE TRACK/ASPECTS OF SURROUNDING FLOW FOR THE COMPACT UPR LOW INITIALLY JUST OFF THE NWRN CORNER OF THE MAINLAND. FOR THE REMAINDER OF THE PERIOD INDIVIDUAL SOLNS TREND RAPIDLY OUT OF PHASE FOR FEATURES ACROSS THE NRN PAC/ALEUTIANS/BERING SEA INTO THE NERN PAC. FOR EXAMPLE WITH AN EMERGING WRN PAC SYSTEM THE 00Z/06Z GFS WERE ON THE FAST SIDE OF THE SPREAD AND THE 00Z ECMWF ON THE SLOW SIDE. MOST 00Z GUIDANCE WEAKENED/PROGRESSED THE INITIAL CNTRL ALEUTIANS SYSTEM TO A GREATER DEGREE THAN 06Z/12Z GFS RUNS. RECENTLY ARRIVED 12Z CMC/UKMET/ECMWF RUNS NOW ADD TO THE POTENTIAL THAT THE ALEUTIANS/BERING SYSTEM MAY BE MORE PERSISTENT THAN PREVIOUSLY FCST. LATER IN THE PERIOD THE POOR RUN TO RUN CONTINUITY IS MOST SIMPLY REPRESENTED BY THE PAST TWO ECMWF RUNS, THE 00Z VERSION SHOWING A BERING SEA CLOSED LOW ALOFT AS OF 12Z SAT BUT THE 12Z/26 RUN DEPICTING A STRONG RIDGE. GFS RUNS SHOW SIMILAR VARIABILITY OVER THE PAST 24-36 HRS. DOWNSTREAM THE 00Z GFS APPEARS TO HAVE THE LEAST PROBABLE EVOLUTION WITH A STRONG SHRTWV REACHING THE SERN COAST/PANHANDLE AS OF 12Z SAT AND SUBSEQUENT NEWD PROGRESSION AS A CLOSED LOW, RIGHT INTO THE MEAN RIDGE DEPICTED BY THE MAJORITY OF GUIDANCE. DUE TO THE RAPIDLY INCREASING SOLN SPREAD, PREFERENCE QUICKLY ADJUSTS TOWARD THE 00Z NAEFS/ECMWF MEANS AND 06Z GEFS MEANS DAYS 6-8 FRI-SUN AFTER A DAY 5 MODEL/ENSEMBLE MEAN TRANSITION. THIS WOULD KEEP LOW PRESSURE LINGERING A LITTLE S OF KODIAK ISLAND, WITH A POTENTIAL WWD SHIFT IN OVERALL MEAN LOW PRESSURE LATE IN THE PERIOD WITH THE ARRIVAL OF UPSTREAM ENERGY. THE FCST PROVIDES REASONABLE CONTINUITY WHILE WAITING FOR BETTER AGREEMENT ON SIGNIFICANT FEATURES, WHOSE APPARENT TRENDS IN NEW 12Z GUIDANCE MAY OR MAY NOT PERSIST CONSIDERING THE VARIABILITY/SPREAD SEEN THUS FAR. RAUSCH