ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 111 PM EST SAT JAN 23 2016 VALID 12Z WED JAN 27 2016 - 12Z SUN JAN 31 2016 IN TERMS OF THE LARGE SCALE EVOLUTION THE LATEST GUIDANCE IS CONSISTENT IN SHOWING A CHANGE IN THE PATTERN OVER THE COURSE OF THE PERIOD. THE INITIAL CONFIGURATION WILL FEATURE A RIDGE EXTENDING N-NW FROM WRN CANADA AND AN AXIS OF LOW HGTS... CONTAINING A COUPLE UPR LOW CENTERS... FROM THE SRN BERING SEA TO S OF THE ALASKA PENINSULA. THEN AN INCREASINGLY SHARP/AMPLIFIED RIDGE SHOULD BUILD FROM THE NERN PAC THROUGH THE MAINLAND AS A STRONG SYSTEM EMERGING FROM ERN ASIA TRACKS NEAR THE WRN-CNTRL ALEUTIANS LATE NEXT WEEK INTO THE WEEKEND. THE FULL ENVELOPE OF GUIDANCE APPEARS TO BE NO BETTER CLUSTERED AND PERHAPS EVEN SLIGHTLY MORE DIVERSE THAN 24 HRS AGO WITH THE STRONG SYSTEM TO THE S OF THE ALASKA PENINSULA AS OF 12Z DAY 4 WED. SPREAD INCREASES WITH TIME AS ENERGY ASSOC WITH THIS SYSTEM COULD BECOME EMBEDDED WITHIN THE ANTICIPATED PATTERN CHANGE. ONE OR MORE INDIVIDUAL SOLNS LIKE THE 06Z GFS OFFER POTENTIAL FOR THE FEATURE TO GET STUCK TO THE S-E OF THE PENINSULA AND ULTIMATELY GET CARRIED AWAY TO THE E AS THE UPSTREAM PATTERN AMPLIFIES. SOME TYPE OF SPLIT OF THE INITIAL SYSTEM IS ANOTHER PSBL SCENARIO AS DEPICTED IN THE 12Z GFS. THERE HAS BEEN A SLIGHTLY FASTER TREND AT SOME VALID TIMES IN THE NEWEST RUNS BUT THE ENSEMBLE MEANS HAVE BEEN CONSISTENT IN KEEPING A MORE CONSOLIDATED SYSTEM WITH MODERATE PROGRESSION AND A TRACK ACROSS THE PENINSULA INTO THE SERN BERING SEA NEAR THE SWRN COAST OF THE MAINLAND. AT LEAST FOR PERIODS OF TIME IN RECENT WEEKS THE ENSEMBLE MEANS HAVE TENDED TO PERFORM BETTER WHEN THERE HAS BEEN CONSIDERABLE MODEL SPREAD SO WOULD LIKE TO MAINTAIN REASONABLE CONTINUITY AS PER THE ENSEMBLE MEANS. THE 00Z ECMWF IS FAIRLY CLOSE TO THE MEANS SO IT IS REASONABLE TO INCLUDE ITS SOLN AS PART OF THE FCST. MEANWHILE THE GENERAL SIGNALS ARE CONSISTENT FOR THE STRONG LARGE SCALE SYSTEM EXPECTED TO TRACK NEAR THE WRN-CNTRL ALEUTIANS FROM LATE THU ONWARD AND BE THE ANCHOR FOR AN UPR TROUGH/AXIS OF LOWER SFC PRESSURES THAT SHOULD BECOME MORE NEGATIVELY TILTED WITH TIME. AS IN PREVIOUS DAYS OPERATIONAL MODEL RUNS ARE SHOWING TOO MUCH VARIABILITY/SPREAD WITH INDIVIDUAL SFC LOW CENTERS TO INCLUDE IN A DETERMINISTIC FCST WITH ANY DEGREE OF CONFIDENCE. THUS PREFER TO MAINTAIN PRIMARY EMPHASIS ON THE MORE CONSOLIDATED AND AGREEABLE/STABLE ENSEMBLE MEANS FOR THE TIME BEING. BASED ON THE FAVORABLE COMPARISON TO THE ENSEMBLE MEANS FOR THE SYSTEM INITIALLY S OF THE ALASKA PENINSULA... FROM DAY 4 WED INTO DAY 5 THU THE 00Z ECMWF HAS HALF WEIGHTING IN THE BLEND WITH THE REST CONSISTING OF THE 06Z GEFS/00Z ECMWF MEANS. THEN ECMWF WEIGHTING IS STEADILY REDUCED AS THE ALEUTIANS SYSTEM BECOMES DOMINANT WITH THE TWO MEANS EVENLY WEIGHTED EXCLUSIVELY BY DAYS 7-8 SAT-SUN. SFC DIFFS ARE LESS PRONOUNCED OVER THE MAINLAND/ARCTIC BUT THE FAVORED ENSEMBLE MEANS ALSO SIDESTEP CONSIDERABLE DETAIL DIFFS ALOFT OVER THESE AREAS. RAUSCH