ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 248 PM EDT FRI MAR 13 2015 VALID 12Z TUE MAR 17 2015 - 12Z SAT MAR 21 2015 THE FCST FOR THE LARGE SCALE PATTERN REMAINS CONSISTENT... WITH A MEAN RIDGE OVER WRN CANADA AND MAINLAND ALASKA WHILE TROUGHING PERSISTS TO THE SW OF THE RIDGE. WITHIN THE MEAN TROUGH THE PRIMARY FEATURE OF NOTE WILL BE AN UPR LOW TO THE S/SW OF THE AK PENINSULA FROM TUE THROUGH AT LEAST THU. THE UPR LOW MAY OPEN UP SHORTLY THEREAFTER AS UPSTREAM NRN PAC ENERGY FEEDS INTO THE MEAN TROUGH POSN. PERHAPS TO A GREATER EXTENT THAN YDAY INDIVIDUAL MODEL RUNS ARE SUGGESTING THAT SMALLER SCALE WAVE DETAILS WITH LOW PREDICTABILITY MAY CAUSE SIGNIFICANT LOCALIZED CHALLENGES FROM THE ERN TO NRN PERIPHERY OF THE SLOW MOVING MEAN UPR LOW TO THE S/SW OF THE AK PENINSULA. OVERALL PREFERENCE IS TO BALANCE CONTINUITY AND DEPICTION OF THE HIGHER CONFIDENCE MEAN PATTERN VS SOME FINER DETAIL WHICH ENOUGH MODEL RUNS SUGGEST WILL EXIST IN ONE FORM OR ANOTHER FROM THE NERN PAC INTO THE PENINSULA/ERN ALEUTIANS. THE FORMER IS BEST ACHIEVED BY INCLUDING 40 PCT OF THE 00Z ECMWF MEAN THROUGH THE PERIOD ALONG WITH ANOTHER 20 PCT OF THE 00Z NAEFS MEAN DAYS 4-5 TUE-WED/06Z GEFS MEAN DAYS 6-8 THU-SAT. THESE SOLNS ARE FAIRLY CONSISTENT FROM YDAY WITH THE TRACK OF THE INITIAL SFC LOW WELL S/SW OF THE PENINSULA... CORRESPONDING THE UPR LOW... IN CONTRAST TO RECENT GFS/GEFS RUNS THAT HAVE TENDED TO BRING THE SFC LOW FARTHER N/NE. THE 06Z GEFS MEAN CONVERGES WITH THE ECMWF MEAN BY THE LATTER HALF OF THE PERIOD WHILE THE NAEFS MEAN DIVERGES FROM THE BEST CLUSTERING UPSTREAM OVER THE PAC. FOR THE REMAINING 40 PCT OPERATIONAL COMPONENT THE 00Z ECMWF IS USED FOR THE FIRST TWO DAYS AS IT FITS WITH CONTINUITY AND THE MODEST MAJORITY CLUSTER FOR THE PARENT SFC LOW AND OFFERS THE MOST REASONABLE DETAIL FOR A WEAK WAVY FRONT HEADING TOWARD THE PANHANDLE ON TUE. THEN BY THU-SAT THE 06Z GFS/00Z ECMWF ARE GIVEN EQUAL CONSIDERATION TO ENHANCE THE ENSEMBLE MEAN BASE PARTIALLY TOWARD ONE WAVE BRUSHING KODIAK ISLAND AROUND 12Z THU AND ANOTHER REACHING E OF KODIAK ISLAND BY 12Z SAT. THERE IS AN INTERVENING WAVE OFF THE PANHANDLE/SRN COAST IN THE 00Z ECMWF BUT IT IS SUFFICIENTLY DOWNPLAYED BY ITS LOW OVERALL WEIGHTING IN THE BLEND. CONFIDENCE WITH DETAILS OF UPSTREAM PACIFIC FLOW RAPIDLY DECLINES AFTER DAY 5 WED. THIS IS DUE TO THE LOW AMPLITUDE/PROGRESSIVE NATURE OF THE MEAN FLOW MAKING IT DIFFICULT TO DETERMINE TIMING AND STRENGTH OF INDIVIDUAL SHRTWVS. NO PIECE OF GUIDANCE INCL THE ENSEMBLE MEANS HAS BEEN VERY CONSISTENT OVER THE PAST DAY AND INDIVIDUAL MODEL RUNS ARE VARIABLE AS WELL. THE BEST CLUSTERING THAT CURRENTLY EXISTS IS AMONG THE 06Z GFS/GEFS MEAN AND 00Z ECMWF/ECMWF MEAN WITH A PROGRESSIVE SYSTEM THAT TRACKS FAR ENOUGH SWD TO HAVE LITTLE INFLUENCE ON THE ALEUTIANS. THE BLENDS FAVORED IN THE PREVIOUS SECTION REFLECT THIS MAJORITY CLUSTERING. RAUSCH