ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 257 PM EDT SUN MAY 21 2017 VALID 12Z THU MAY 25 2017 - 12Z MON MAY 29 2017 THE DAYS 4-8 FORECAST FOR ALASKA IS DOMINATED BY A DEEP LAYER TROUGH OVER THE BERING SEA AND DOWNSTREAM RIDGE OVER THE NORTH PACIFIC AND GULF OF AK INTO THE AK PANHANDLE. MANUAL PROGS BLENDED THE OPERATIONAL MODEL GUIDANCE (12Z GFS AND 00Z ECMWF)WITH THEIR ENSEMBLE MEANS (06Z GEFS AND 00Z ECMWF) FOR DAYS 4 THU 25 MAY THROUGH DAY 6 SAT 27 MAY...WITH MORE WEIGHTING ON THE ENSEMBLE MEANS DAYS 7 SUN 28 MAY AND DAY 8 MON 29 MAY. THE OPERATIONAL RUNS AND ENSEMBLES AGREE ON A NORTHEASTERN BERING SEA LOW ON DAY 4 /THU 25 MAY STARTING NEAR THE BERING STRAIT AND MOVING NORTH AND WEAKENING AS IT MOVES INTO THE ARCTIC OCEAN...WITH A FRONT EXTENDING EAST ACROSS NORTHERN AK. THE 12Z GFS WAS ON THE FAST SIDE OF THE GUIDANCE DISTRIBUTION...WITH THE PRIOR 06 AND 00Z GFS RUNS CLUSTERING BETTER WITH THE 06Z GEFS MEAN AND 00Z ECMWF MEAN. A BLENDED SOLUTION INCORPORATING THE PRIOR GFS RUNS ALONG WITH THE 00Z ECMWF AND 06Z GEFS ENSEMBLE MEANS WAS USED. THE MODELS SHOWED A SLIGHTLY DEEPER LOW...SO THE BLEND MAINTAINED SOME OF THE STRENGTH OF THE LOWS. NEXT WEEKEND INTO EARLY NEXT WEEK SHOWS A GROWING SPREAD OF SOLUTIONS AS THE MODELS AND ENSEMBLES FORECAST CYCLONES WILL DEVELOP IN THE VICINITY OF THE KAMCHATKA PENINSULA AND MOVE EAST NORTHEAST INTO THE SOUTHERN BERING SEA/ALEUTIANS/OR NORTHERN PACIFIC. THE 00-12Z GFS AND 12Z-00Z ECMWF SHOWED SIGNIFICANT RUN TO RUN CHANGES IN CYCLONE TRACK AND INTENSITY. THE DISPLAY OF PLOTTED SURFACE LOWS OF THE CANADIAN/ECMWF/GEFS ENSEMBLE MEMBERS RESEMBLES A STRING OF PEARLS...WIT LITTLE OVERLAP/CLUSTERING OF SOLUTIONS. GIVEN THE LACK OF RUN TO RUN CONTINUITY (I.E. THE 12Z SUN RUN OF THE ECMWF MOVED THE LOW PRESSURE CENTER 700 NM SOUTHEAST AT 12Z MON 29 MAY AS COMPARED TO ITS 00Z RUN)...THERE IS LITTLE CONFIDENCE IN AN OPERATIONAL RUN. CONSEQUENTLY...GREATER WEIGHTING WAS GIVEN TO THE MEANS...WHICH AS USUAL OVERLAP BETTER ON THE AXIS/ORIENTATION OF LOW PRESSURE. LOWS WITHING THE BROADER CYCLONIC ENVELOPE WILL EVENTUALLY GET BETTER DEFINED. THE PARADE OF LOWS IN THE BERING SEA SUPPORTS BUILDING THE DOWNSTREAM HIGH AMPLITUDE RIDGE ACROSS THE NORTH PACIFIC INTO EASTERN AK/PANHANDLE...WITH ONLY MINOR DIFFERENCES AMONG THE MODELS AND ENSEMBLES. THIS SUPPORTS A DRY PATTERN ACROSS EASTERN TO SOUTHEASTERN AK/AK PANHANDLE. DOWNSTREAM UNDER THE UPPER RIDGE...TEMPERATURES ARE EXPECTED TO BE ABOVE NORMAL IN EASTERN AK TO THE PANHANDLE. UNDER THE INITIAL TROUGH IN NORTHWEST AK TEMPERATURE ARE EXPECTED TO BE BELOW NORMAL BUT AS IT DEAMPLIFIES OVER THE WEEKEND...THE AIRMASS MODERATES SO THE NEGATIVE ANOMALIES HAVE DISSIPATED BY EARLY NEXT WEEK...SO TEMPERATURES RETURN TO NEAR OR SLIGHTLY ABOVE NORMAL IN NORTHWEST AK. PETERSEN