ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 226 PM EDT SUN JUL 17 2016 VALID 12Z THU JUL 21 2016 - 12Z MON JUL 25 2016 THE COMBINATION OF CLOSED LOW ENERGY HEADING TOWARD THE MAINLAND FROM THE BERING SEA ON THU ALONG WITH FLOW TO THE N WILL HELP TO FORM A MEAN TROUGH FCST TO EXTEND FROM THE MAINLAND INTO THE NERN PACIFIC. THE EXTENT TO WHICH THIS TROUGH PERSISTS BY THE END OF THE PERIOD WILL BE DETERMINED BY THE STRENGTH AND TIMING OF UPSTREAM ENERGY THAT MAY APPROACH THE MAINLAND AND/OR BERING SEA FROM ERN SIBERIA. MEANWHILE THE NERN PART OF THE MAINLAND SHOULD REMAIN UNDER THE WRN PERIPHERY OF AN INCREASINGLY ELONGATED MEAN UPR LOW POSITIONED OVER EXTREME NRN CANADA. GUIDANCE IS OSCILLATING FOR TIMING OF THE INITIAL BERING SEA SYSTEM. AS A WHOLE TODAY'S SOLNS REPRESENT A SLOWER ADJUSTMENT FROM 24 HRS AGO VERSUS A FASTER TREND LEADING INTO YDAY'S FCST. THROUGH THE 00Z/06Z CYCLES THE 06Z GFS AND 00Z ECMWF/UKMET/CMC REPRESENTED THE BEST CLUSTER WITH THE 00Z GFS SLIGHTLY SLOWER. LEADING RIDGE COULD SUPPORT SLOWER 00Z GFS TIMING BUT MULTI-DAY INCONSISTENCY SEEMS TO FAVOR ADJUSTING ONLY TO THE EXTENT OF THE MAJORITY SOLN. THE 12Z GFS FALLS IN LINE WITH THE MAJORITY AS DOES THE 12Z CMC BUT THE UKMET TRENDS FASTER AFTER 12Z THU. FOR DAYS 4-5 THU-FRI A BLEND OF HALF 00Z ECMWF AND THE REMAINDER 06Z/12Z GFS RUNS REPRESENTS CONSENSUS WELL. DURING THE LATTER HALF OF THE PERIOD THE OPERATIONAL MODEL RUNS ARE NOTICEABLY MORE PRONOUNCED THAN THE MEANS WITH THE STRENGTH OF ENERGY ALOFT AND ASSOC SFC REFLECTION EMERGING FROM ERN SIBERIA AND POTENTIALLY HAVING AN INFLUENCE ON THE WRN MAINLAND BY THE START OF NEXT WEEK. HOWEVER GUIDANCE SPREAD AND RUN TO RUN VARIABILITY ARE SUFFICIENTLY GREAT AT THIS TIME TO FAVOR A SOLN CLOSER TO THE ENSEMBLE MEANS UNTIL BETTER AGREEMENT DEVELOPS. WHAT SIGNAL THERE IS SUGGESTS THE TRACK OF ANY WELL DEFINED SFC LOW SHOULD BE WITHIN A FEW DEGS LATITUDE OF 65N INSTEAD OF FARTHER S AS IN THE 00Z GFS. GIVEN THESE CONSIDERATIONS THE FCST BLEND INCORPORATES STEADILY INCREASING ENSEMBLE MEAN WEIGHTING SAT-MON WITH DAY 8 USING THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS EXCLUSIVELY. OVER RECENT DAYS THE ENSEMBLE MEANS HAVE TENDED TO BE MOST STABLE FOR THE HANDLING OF HIGH LATITUDE FLOW AFFECTING THE NERN MAINLAND. SOME INDIVIDUAL GFS/ECMWF RUNS HAD BROUGHT RELATIVELY LOW HGTS TOWARD THE NERN MAINLAND IN SOME FASHION BUT LATER RUNS WOULD TREND TOWARD A MORE MODERATE SCENARIO. THERE ARE STILL MEANINGFUL DETAIL DIFFS TODAY BUT WITH LESS SIGNIFICANT IMPACT ON THE NERN MAINLAND. RAUSCH