ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 PM EDT FRI JUN 19 2015 VALID 12Z TUE JUN 23 2015 - 12Z SAT JUN 27 2015 LATEST GUIDANCE GENERALLY MAINTAINS THE THEME OF A SLOWLY EVOLVING BLOCKY PATTERN BUT WITH UNCERTAINTY IN SOME ASPECTS OF THE FCST. OVER THE PAST DAY THE ENSEMBLE MEANS HAVE BEEN THE MOST STABLE IN DEPICTING AN UPR RIDGE CNTRD NEAR THE NRN BERING SEA AND LIKELY EXTENDING EWD ACROSS A MAJORITY OF THE SRN HALF OF THE MAINLAND WHILE MORE PROGRESSIVE AND AT TIMES BROADLY CYCLONIC FLOW PREVAILS ACROSS THE NRN MAINLAND INTO NWRN CANADA. A MEAN SFC FRONT SHOULD EXTEND ALONG THE SRN SIDE OF THIS BAND OF PROGRESSIVE FLOW. FARTHER SWD THERE SHOULD BE TWO SLOW MOVING UPR LOWS... ONE TO THE S OF THE ALASKA PENINSULA WITHIN A FEW DEGS LATITUDE OF 50N AND A SECOND COMING INTO THE PICTURE W OF THE ALEUTIANS. OVER THE PAST 2-3 DAYS OPERATIONAL MODEL RUNS HAVE VARIED AMONG EACH OTHER AND FROM RUN TO RUN WITH THE EVOLUTION OF THE UPR RIDGE/RESULTING DOWNSTREAM FLOW AS WELL AS WITH WAVE DETAILS IN THE OVERALL AREA OF MEAN LOW PRES OVER THE NERN PAC. AMONG LATEST SOLNS THE 00Z ECMWF DOES NOT COMPARE WELL TO MOST 00Z ENSEMBLE MEMBERS... INCL FROM THE ECMWF PACKAGE... WITH ITS RELATIVELY STRONG/SLOW MOVING MAINLAND TROUGH IN THE WED-FRI TIME FRAME. AT LEAST THE 06Z GFS WAS SOMEWHAT WEAKER/FASTER WITH ITS TROUGH. THE 00Z ECMWF ALSO TRENDS TO THE SRN PART OF THE SPREAD WITH THE NERN PAC SYSTEM. THUS WOULD BE QUITE RELUCTANT TO INCLUDE ANY OF THE 00Z ECMWF IN THE FCST. THE 12Z GFS HAS FAVORABLY TRENDED TOWARD THE MEANS ACROSS THE MAINLAND/BERING SEA... DIVERTING HIGHER LATITUDE SHRTWV ENERGY MORE INTO WRN CANADA WHILE NOT BRINGING THE UPR RIDGE AS FAR EWD AS FCST BY THE 00Z GFS BY FRI. THE 12Z GFS BRINGS THE NERN PAC SYSTEM SOMEWHAT SWWD OF CONSENSUS BY LATE IN THE WEEK THOUGH. FOR THE SYSTEM NEARING THE WRN ALEUTIANS LATE IN THE PERIOD THE MEANS HAVE CONVERGED FAIRLY WELL ON TIMING... MORE FROM THE GEFS MEAN SLOWING DOWN TOWARD THE ECMWF MEAN. OPERATIONAL RUNS CURRENTLY SHOW BETTER THAN AVG AGREEMENT FOR THE TIME FRAME INVOLVED BUT SUGGEST THE POTENTIAL FOR SYSTEM EVOLUTION TO BE MORE COMPLEX THAN DEPICTED IN THE MEANS. GIVEN TYPICAL DAYS 7-8 VERIFICATION THE ENSEMBLE MEANS DEPICT SYSTEM EXISTENCE SUFFICIENTLY WELL WHILE WAITING TO SEE IF OPERATIONAL MODELS ESTABLISH REASONABLE CLUSTERING/CONTINUITY OVER MULTIPLE CYCLES. DURING THE EARLY AND MIDDLE PART OF THE FCST THE FAVORED BLEND PRIMARILY USES THE 00Z ECMWF MEAN AND 12Z GFS WITH SLIGHT WEIGHTING OF THE 00Z NAEFS MEAN... AS THE 12Z GFS COMPARES BEST TO THE MEANS EARLY-MID PERIOD AND THE ECMWF MEAN GENERALLY HAS THE BEST DEFINED SOLN FOR MOST FEATURES. THE NAEFS MEAN RANKS SECOND IN TERMS OF DEFINITION. THE FCST GRADUALLY DECREASES 12Z GFS WEIGHTING AROUND THU-FRI AS DETAIL CONFIDENCE DECLINES... LEADING TO A 70/30 WEIGHTING OF THE ECMWF/NAEFS MEANS BY DAY 8 SAT. RAUSCH