ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 431 PM EDT THU JUL 21 2016 VALID 12Z MON JUL 25 2016 - 12Z FRI JUL 29 2016 ...PATTERN OVERVIEW/GUIDANCE AND UNCERTAINTY AND WEATHER/THREAT HIGHLIGHTS... ON THE LARGE SCALE...THE OVERALL PATTERN IS RELATIVELY PREDICTABLE AS A MEAN TROUGH WILL BE CONTINUALLY REINFORCED OVER WESTERN ALASKA AND THE ADJACENT GULF. AS USUAL...THE DEVIL IS IN THE DETAILS BUT AT LEAST THE LATEST 12Z GFS/ECMWF HAVE SOMEWHAT SIMILAR SCENARIOS WITH SEVERAL SHORTWAVE FEATURES REESTABLISHING THE MAIN TROUGH...BUT OF COURSE THE RESOLUTION OF THESE INDIVIDUAL FEATURES HAVE POOR CONTINUITY AND LARGE INTER MODEL DIFFERENCES BUT THAT IS TO BE EXPECTED. DESPITE THESE INCONSISTENCIES...THE TROUGH REMAINS A HIGHLY PROBABLE FEATURE AS WELL AS A RIDGE OVER THE NORTH CENTRAL PACIFIC INTO THE BERING SEA AND A SEPARATE RIDGE ALONG THE WESTERN CANADIAN COAST INTO EASTERN ALASKA. ANOTHER AREA OF SIGNIFICANT MODEL DIFFERENCES IS THE MOVEMENT OF SEVERAL SHORTWAVE FEATURES MOVING EAST FROM NORTHEAST SIBERIA THAT SEEM TO HAVE MORE COHERENCY DURING THE MORNING MODEL RUNS. THEREFORE...THE FORECAST FOR THE NORTHERN BERING SEA ACROSS THE NORTH SLOPE IS HIGHLY UNPREDICTABLE LATER IN THE FORECAST WHEN POTENTIAL SHORTWAVE SYSTEMS START TO MOVE EAST. IN GENERAL...THE UNCERTAINTY IN THE FORECAST TROUGH AREA OVER SOUTHWEST ALASKA AND THE NORTHERN GULF IMPLIES THAT RAINY CONDITIONS ARE LIKELY IN THIS KIND OF FLOW REGIME AND THAT ANY SYSTEMS CROSSING NORTHEAST SIBERIA TO THE UPPER BERING SEA AND ARCTIC NORTH OF ALASKA WILL ALSO PLAY A ROLE IN PRECIPITATION GENERATION. KOCIN