ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 359 PM EDT WED MAY 31 2017 VALID 12Z SUN JUN 4 2017 - 12Z THU JUN 8 2017 MODELS AND ENSEMBLES CONTINUE TO INDICATE A STRONG SIGNAL IN FORMING A PAIR OF CLOSED LOWS ACROSS THE NORTHEASTERN PACIFIC THIS WEEKEND. THE LEAD FEATURE IS FORECAST TO PIVOT BACK TOWARD THE NORTH AND WEST ALLOWING IT TO APPROACH THE SOUTH-CENTRAL ALASKA COAST BY SUNDAY AFTERNOON. EVENTUALLY THE TRAILING UPPER LOW BEGINS TO TAKE OVER AS THE DOMINANT SYSTEM AS MODELS DEEPEN THE FEATURE CONSIDERABLY TOWARD THE END OF THE WEEKEND. THIS WILL ALLOW BROAD CYCLONIC FLOW TO DOMINATE MUCH OF THE NORTHEASTERN PACIFIC INTO EARLY NEXT WEEK. UPPER LEVEL RIDGING IS EXPECTED FROM EASTERN RUSSIA AND ACROSS NORTHERN ALASKA, WITH A SURFACE HIGH NORTH OF THE ARCTIC COAST. MODEL DETAILS DIFFER IN HOW MUCH OF THE SHORTWAVE ENERGY TO THE SOUTH WILL INTERFERE WITH THE BUILDING RIDGE TO THE NORTH. THERE IS ALSO DECENT AGREEMENT THAT ANOTHER LARGE UPPER LOW OVER THE WESTERN ALEUTIANS AND SOUTHERN BERING SEA WILL MATERIALIZE BY THE SECOND HALF OF THE FORECAST PERIOD. GIVEN DECENT SYNOPTIC AGREEMENT ACROSS THE BOARD, MORE OF THE DETERMINISTIC 12Z GFS AND 00Z ECMWF WAS INCORPORATED INTO THE FORECAST THAN IS NORMALLY THE CASE. THE FORECAST GENERALLY SPLIT THE DIFFERENCE BETWEEN THE 12Z GFS/00Z ECMWF EARLY ON BEFORE TRANSITIONING MORE TOWARD ENSEMBLE MEANS BY THE MIDDLE OF NEXT WEEK. THE UPCOMING PATTERN SUNDAY AND INTO NEXT WEEK BE QUITE MILD OVER THE CENTRAL AND SOUTHERN INTERIOR REGIONS AS HIGHS ARE EXPECTED TO BE IN THE MIDDLE 60S TO LOWER 70S AT THE LOWER ELEVATIONS THROUGHOUT THIS TIME PERIOD. THE ARCTIC COAST REGION IS EXPECTED TO REMAIN QUITE CHILLY WITH PERSISTENT NORTHEASTERLY WINDS OFF THE ARCTIC OCEAN. ON THE SOUTHERN COAST, EASTERLY FLOW COUPLED WITH SHORTWAVES PIVOTING AROUND THE MAIN UPPER LOW OVER THE GULF OF ALASKA WILL PROVIDE ENOUGH FORCING FOR MAINLY DIURNALLY DRIVEN SHOWERS AND A FEW THUNDERSTORMS, ESPECIALLY OVER TERRAIN FAVORED AREAS. HAMRICK