ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 151 PM EST MON FEB 27 2017 VALID 12Z FRI MAR 03 2017 - 12Z TUE MAR 07 2017 THE MAJORITY OF GUIDANCE AGREES FAIRLY WELL IN SHOWING A MILD RETROGRESSION OF LARGE SCALE FEATURES... WITH A STRONG CNTRL BERING SEA RIDGE/UPR HIGH DRIFTING TO THE WRN BERING SEA/ERN SIBERIA AND ALLOWING FOR A DEEPENING MEAN TROUGH TO EVOLVE OVER MAINLAND ALASKA AND THE NERN PAC/GULF OF ALASKA. AMONG INDIVIDUAL SOLNS THERE IS STILL SOME DISAGREEMENT OVER EXTENT OF WWD MOTION FOR THE UPR RIDGE. OTHER QUESTION MARKS EXIST FOR SHRTWV DETAILS EARLY IN THE PERIOD AND SPECIFICS OF NERN PAC/GULF OF ALASKA LOW LOW PRESSURE THAT SHOULD BE DEEPENING LATE IN THE PERIOD. DURING DAYS 4-5 FRI-SAT THE PRIMARY DIFFS ARE WITH SHRTWV ENERGY FLOWING BTWN THE BERING SEA/ERN SIBERIA RIDGE AND DEEP UPR LOW TO THE NE OF THE MAINLAND. THE RELATIVELY SMALL SCALE OF INDIVIDUAL SHRTWVS TYPICALLY LEADS TO LOW PREDICTABILITY FOR SPECIFICS EVEN IN THE EARLY EXTENDED TIME FRAME. FOR THIS PART OF THE FCST THE INITIAL BLEND USED THE 00Z ECMWF/GFS/CMC TO REPRESENT COMMON ASPECTS OF THE FCST SFC/ALOFT WITH BETTER DEFINITION THAN THE ENSEMBLE MEANS. BY DAYS 5-7 SUN-TUE THE MOST SIGNIFICANT DISCREPANCIES INVOLVE BERING SEA/SIBERIA RIDGE POSN AND MAINLAND/NERN PAC TROUGHING PLUS DETAILS OF ASSOC GULF OF ALASKA SFC LOW EVOLUTION. FOR THE RIDGE THE LATEST GEFS/ECMWF/CMC ENSEMBLE MEANS OFFERED THE MOST SUPPORT FOR A FARTHER W POSN THAN 00Z/06Z/12Z GFS RUNS AND PERHAPS THE 00Z CMC. WHILE THERE IS CONSIDERABLE SPREAD IN DETAILS FOR THE MAINLAND/NERN PAC TROUGH... THE ENSEMBLE MEANS ARE SHOWING A NOTICEABLY DEEPER SIGNAL ALOFT WITH GULF OF ALASKA LOW PRES ALSO TRENDING DEEPER. OVER THE PAST 1-2 DAYS ECMWF MEAN RUNS HAVE BEEN MORE CONSISTENT WITH THE OVERALL RIDGE/TROUGH PATTERN AND MORE STEADY WITH THE DEEPENING TREND FOR THE UPR TROUGH/SFC LOW PRES. BASED ON THESE TRENDS IT SEEMED REASONABLE TO START OUT WITH AN UPR TROUGH/SFC LOW DEPTH BTWN OPERATIONAL GUIDANCE AND THE WEAKER ENSEMBLE MEANS AS THE BEST WAY TO BALANCE THE AGREEABLE MEAN PATTERN AND DETAIL UNCERTAINTY. VARIOUS SCENARIOS ARE PSBL FOR EXACT EVOLUTION OF THE GULF OF ALASKA SFC LOW INCLUDING IN-PLACE DEEPENING (00Z CMC) OR MULTI-LOW INTERACTION INCLUDING A LEADING FEATURE NEAR HAIDA GWAII (12Z GFS) IN RESPONSE TO DIGGING TROUGH/CLOSED LOW ENERGY... OR INTERACTION WITH A MID-LATITUDE PAC WAVE APPROACHING FROM THE SW (00Z GFS/ECMWF/ECMWF MEAN). WHICH EVOLUTION ULTIMATELY OCCURS WILL IMPACT THE AMOUNT OF MOISTURE THAT REACHES THE SRN COAST/PANHANDLE REGION. RAUSCH