Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 544 PM EST Wed Jan 01 2020 Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020 A persistent upper-level mean trough centered across the interior of Alaska is forecast by most guidance to continue through the extended forecast period, ensuring a continued period of well below-average temperatures. Between the trough/upper low across Alaska and a building ridge across the north central Pacific, an active storm track should persist from northeast Asia, near/south of the Aleutians, and into the Gulf of Alaska. The ECMWF/CMC were the solutions most closely clustered with the ensemble consensus during days 4-5 (Sun-Mon) with a low pressure system forecast to enter/cross the Gulf of Alaska as it moves toward Southeast Alaska. The GFS has shown run-to-run continuity issues and was not preferred for use in a blend. Thus, a blend of the 12Z ECMWF/CMC was heavily used during days 4-5, along with a small component of the 00Z ECENS mean. Model spread was a bit higher with the next in the series of low pressure systems, forecast to near the western Aleutians by late Mon/early Tue. Models do show some consensus that this could be quite deep, with even the ensemble means showing a low into the 970s by early Tue, but solutions differ on the track of what appears to be a rather complex and chaotic evolution, potentially featuring at least a couple areas of low pressure. Farther north across the Interior and the North Slope, the ECMWF/CMC and ensemble means showed general consensus that upper troughing should remain in place, while the GFS attempts to bring an upper high from the Arctic Ocean southward into Alaska where it interacts with shortwave ridging in the Gulf to develop a weak ridge axis across Alaska. The GFS solution was not preferred here either, and WPC favored the idea shown by the ECMWF/CMC of keeping the Arctic and North Pacific streams more separate, as the upper trough over the Interior and the intense cold air at the lower levels should be somewhat difficult to expel. Thus, the forecast during days 6-8 (Tue-Thu) made use of gradually increasing and majority ECENS ensemble mean, along with diminishing use of the ECMWF/CMC through time. This pattern should result in a continuation of well below average temperatures across much of mainland Alaska, with max and min temperatures, especially across the Interior as well as southwestern portions of mainland Alaska as much as 20-30 deg F below average. The active storm track from the Aleutians into the Gulf of Alaska should keep chances for precipitation fairly high from extreme southeastern portions of mainland Alaska into the Panhandle/Southeast Alaska, as well as across the Aleutians, through the extended forecast period. Ryan Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Much below normal temperatures across portions of mainland Alaska, Sat-Wed, Jan 4-Jan 8. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html