Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 147 PM EST Wed Dec 19 2018 Valid 12Z Sun Dec 23 2018 - 12Z Thu Dec 27 2018 ...Guidance/Predictability Assessment and Preference... Latest guidance continues to offer a reasonably similar larger scale pattern evolution for much of the next week, but still differ significantly with the amplitude and timing of embedded small-mid scale systems days 4-8. Accordingly decided after coordination with Alaskan NWS weather forecast offices to primarily derive the WPC medium range Alaskan forecast from a blend of compatable GEFS/NAEFS/ECMWF ensemble means along with input from the National Blend of Models. This solution maintains good WPC continuity. ...Weather/Threats Highlights... The main storm track over the next week includes a series of organized low pressure systems and frontal systems that track along/south of the Aleutians and the Alaska Peninsula then into the Gulf of Alaska and southern Bering Sea. These lows present both a maritime hazard and a periodic heavy precipitation threat throughout the next week for the Aleutians/AKpen/Southwest Alaska and southern/southeastern Alaska. Individual system timing and strength remains quite variable in guidance, but the overall storm track seems reasonable. In this pattern, a lead system exiting the eastern Gulf of Alaska Sunday is replaced upstream with a set of lows from the Aleutians that are supported by an amplifying mid-upper level mean trough. The lows are expected to effect the southern Bering Sea and the Gulf of Alaskan next week and activity may divert increasingly inland over time channeling between the supporting mean trough and building downstream upper ridge over time. Overtop, forecast guidance remains uncertain but has become better clustered overall with the depiction of the pattern over the North Slope/Interior and Bering Sea days 4-8. Shortwave trough/closed low energy aloft tends to favor a weakness aloft from the North Slope to the Bering Strait that may support some light snows. Schichtel WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html