ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 326 PM EDT FRI AUG 25 2017 VALID 12Z TUE AUG 29 2017 - 12Z SAT SEP 02 2017 A COMPLEX FLOW PATTERN WILL PERSIST ACROSS ALASKA THROUGH DAYS 4-8 (TUE-FRI), WITH UPPER-LEVEL ENERGY ORIGINATING IN THE HIGH ARCTIC AS WELL AS EASTERN RUSSIA/ASIA INTERACTING AND AFFECTING THE STATE. THE GFS HAS BEEN CONSISTENTLY ON THE WEAK SIDE OF THE SPREAD WITH THE ARCTIC ENERGY ACROSS THE NORTHERN COAST ON DAY 3, AND WHILE IT HAS GRADUALLY TRENDED STRONGER, THIS REMAINS THE CASE. THE MAJORITY OF DETERMINISTIC SOLUTIONS WRAP THIS AREA OF ARCTIC ENERGY SOUTHWESTWARD AND MERGE IT INTO THE BROADER UPPER LOW FARTHER SOUTH, ALTHOUGH SOLUTIONS DIFFER AS TO HOW QUICKLY THIS OCCURS AND WHICH INDIVIDUAL WAVE BECOMES DOMINANT, WHICH RESULTS IN VARYING UPPER LOW EVOLUTIONS. THE SITUATION IS FURTHER COMPLICATED BY A VIGOROUS SHORTWAVE ORIGINATING ACROSS EASTERN RUSSIA WHICH IS FORECAST BY ALL GUIDANCE TO CROSS THE ALEUTIANS ON DAY 4, AFTER WHICH SOME DEGREE OF PHASING OCCURS WITH THE EXISTING UPPER LOW, AND A SURFACE CYCLONE IS FORECAST BY MOST GUIDANCE TO DEVELOP IN THE GULF OF ALASKA. MODELS HAVE COME INTO BETTER AGREEMENT WITH RESPECT TO A MODERATE DEGREE OF PHASING OCCURRING, AND THE ECMWF HAS BACKED OFF ON SHOWING A DEEP CYCLONE IN THE SOUTHEASTERN BERING. ALL DETERMINISTIC SOLUTIONS NOW SHOW A SURFACE LOW OF MODERATE INTENSITY IN THE GULF OF ALASKA DAYS 4-5, WHICH MOVES NORTH INTO THE SOUTHERN AK COAST BY DAY 6. BY LATE IN THE MEDIUM RANGE, ANOTHER VIGOROUS SHORTWAVE IS FORECAST BY THE GFS/ECMWF/CMC TO EMERGE FROM EASTERN RUSSIA/ASIA AND APPROACH THE BERING SEA. GIVEN THE COMPLEX PATTERN, MODELS SHOW DECENT AGREEMENT WITH RESPECT TO THE TIMING OF THIS FEATURE, WITH THE CMC ON THE FAST SIDE OF THE SPREAD (ESPECIALLY BY DAY 8) AND THE GFS ON THE SLOW SIDE. GIVEN THE SOMEWHAT IMPROVED SPREAD FOR DAYS 4-6, ESPECIALLY WITH RESPECT TO THE EVOLUTION OF THE CYCLONE IN THE GULF, A BLEND HEAVILY WEIGHTED TOWARD THE DETERMINISTIC GFS/ECMWF (A BIT MORE TOWARD THE ECMWF GIVEN ITS BETTER HANDLING OF THE ARCTIC ENERGY) IS PREFERRED DURING DAYS 4-5, WITH INCREASED WEIGHTING TOWARD THE ENSEMBLE MEANS (GEFS/ECENS/NAEFS) FROM DAY 6 ONWARD. RYAN