ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 203 PM EDT SAT MAR 29 2014 VALID 12Z WED APR 02 2014 - 12Z SUN APR 06 2014 MOST MEDIUM RANGE GUIDANCE STILL INDICATES A TRANSITION TOWARD HIGHER AMPLITUDE FLOW DOMINATED BY LARGE SCALE FEATURES BY NEXT WEEKEND... WITH THE GREATEST UNCERTAINTY BEING FOR EVOLUTION OF MEDIUM TO SMALLER SCALE FEATURES BEFORE THIS EVOLUTION TAKES PLACE. ENSEMBLE MEANS AGREE FAIRLY WELL THAT ONE MEAN TROUGH SHOULD BECOME ESTABLISHED OVER THE CNTRL/WRN MAINLAND AND SWD WITH ANOTHER POISED TO ENTER THE WRN PAC WHILE A BUILDING RIDGE REACHES NEAR THE DATE LINE. OPERATIONAL MODELS GENERALLY FIT THIS TREND BUT WITH TYPICAL DIFFS IN AXIS POSNS AND DISTRIBUTION OF ENERGY WITHIN THE TROUGHS. DURING DAYS 4-6 WED-FRI... THE 00Z ECMWF IS THE LEAST PREFERRED SOLN WITH A SHORT RANGE NRN PAC/ALEUTIANS SYSTEM WHICH THE MODEL HOLDS FARTHER WWD THAN A LARGE MAJORITY OF MODELS/ENSEMBLE MEMBERS. THIS ASPECT OF 00Z ECMWF EVOLUTION SIGNIFICANTLY AFFECTS DOWNSTREAM FLOW AND INTRODUCES AN INTERACTION WITH THE TRAILING NRN PAC/ALEUTIANS SYSTEM NOT SEEN IN THE CONSENSUS. WITH THIS TRAILING SYSTEM THERE IS FAIR CLUSTERING THOUGH WITH A SOMEWHAT FASTER TREND RELATIVE TO YDAYS PREFERRED CLUSTER. MEANWHILE THERE IS STILL A LOT OF SPREAD WITH THE PATTERN TO THE W/NW OF THE MAINLAND IN ADVANCE OF THE EXPECTED TROUGH AMPLIFICATION. OVER THE PAST COUPLE DAYS THE ECMWF MEAN HAS OSCILLATED IN 12-HRLY RUNS WITH THE 00Z VERSIONS MUCH STRONGER WITH THE RIDGE INITIALLY OVER THE NRN BERING SEA RESULTING IN DELAYED TROUGH DEVELOPMENT. THE LATEST 00Z RUN IS MORE PRONOUNCED IN THIS REGARD. ON THE OTHER SIDE OF THE SPECTRUM THE GFS/GEFS MEAN RUNS HAVE RECENTLY BEEN QUICKEST/DEEPEST WITH TROUGH AMPLIFICATION. FINALLY... CONSENSUS HOLDS FAIRLY WELL WITH NERN PAC LOW PRESSURE LIKELY REMAINING OFFSHORE. THE 00Z/06Z GFS RUNS ARE FAIRLY CLOSE TO THE MIDDLE OF THE ENSEMBLE SPREAD WITH THE 00Z ECMWF MEAN A LITTLE WWD. THE 12Z GFS HAS CHANGED CONSIDERABLY... MUCH STRONGER WITH THE INITIAL BERING SEA RIDGE AND FLATTER WITH NERN PAC FLOW THUS BRINGING THE NERN PAC SFC LOW TO THE PANHANDLE. THIS IS ONE OF MANY PSBL SCENARIOS BUT SO FAR WITH LESS SUPPORT THAN NEEDED TO MERIT INCLUDING IN THE FCST. NOT COUNTING THE 12Z GFS THAT HAS LITTLE MAINLAND TROUGHING AT ALL... BY DAYS 7-8 SAT-SUN THE PRIMARY ISSUE IS PRECISE LONGITUDE OF THE UPR TROUGH WHICH WILL AFFECT LOW PRESSURE FCST E OF KODIAK ISLAND. BEST CONSENSUS OF MODEL/ENS SOLNS... ECMWF MEAN CONTINUITY... AND TELECONNECTIONS RELATIVE TO A CORE OF POSITIVE HGT ANOMALIES FCST NEAR 55N 110E SUGGEST THE TROUGH AXIS MAY BE 5-10 DEGS LONGITUDE W OF THE 00Z ECMWF MEAN. THIS WOULD FAVOR AT LEAST HALF WEIGHTING OF THE 06Z GEFS/00Z NAEFS MEANS ALOFT WITH A SFC LOW POSN A LITTLE WWD OF THE 00Z ECMWF MEAN AS WELL. PRIMARY EMPHASIS TO LEAN AWAY FROM THE 00Z ECMWF/12Z GFS SOLNS WHILE OTHERWISE FAVORING AN INTERMEDIATE APPROACH WITH SOME OPERATIONAL DETAIL WHERE DIFFS EXIST LEAD TO STARTING WITH A BLEND OF 00Z/06Z GFS AND 00Z ECMWF MEAN THROUGH DAY 6 FRI WITH LATE PERIOD CONSIDERATIONS RECOMMENDING A TRANSITION TO A BLEND OF HALF 00Z ECMWF MEAN AND THE REMAINDER 06Z GEFS/00Z NAEFS MEAN THEREAFTER. RAUSCH