Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 607 PM EST Tue Feb 11 2020 Valid 12Z Sat Feb 15 2020 - 12Z Wed Feb 19 2020 An active upper-level jet across the North Pacific will cause a series of relatively deep low pressure systems to progress near the Aleutians and into the Gulf of Alaska during the extended forecast period. Clustering of deterministic solutions and ensemble members was perhaps a bit better than average through the period, despite a fair degree of variability on timing/intensity among deterministic solutions. There were some significant intensity differences on a surface low expected to pass south of the Aleutians and move into the Gulf of Alaska Sat-Sun, with the ECMWF on the strong side and the GFS on the weak side, but general agreement on timing of the system. Thus, a compromise on the intensity of this feature between the ECMWF/GFS seemed reasonable. The described scenario should lend favorably to relatively heavy use of ensemble means fairly early in the extended period. Farther north, the arctic influence across the North Slope and northern portions of the interior looks to persist into at least the middle of next week. A cutoff upper low is shown by most guidance to persist across northern mainland Alaska through Sun or perhaps into Mon before an additional arctic shortwave approaches by the middle of next week. Models/ensemble show agreement on this general idea, despite some differences on the specifics. This lends further utility to a heavily ensemble-based blend. Given the considerations, a blend based on the 12Z ECMWF/GFS was used initially on day 4 (Sat), with a shift to heavier weight on ECENS/NAEFS ensemble means from day 5 (Sun) onward. The Aleutians, southern mainland Alaska, and the Alaska Panhandle will remain subject to frequent round of precipitation during the extended forecast period due to the frequent passage of low pressure systems. Heavy precipitation will be possible for some areas through Tuesday. Additionally, the arctic air mass across the interior and the North Slope will hold strong through much of the forecast period, with high/low temperatures 10 to 20 deg F below average for many areas. Meanwhile, areas across the Aleutians, southern mainland, and Southeast Alaska will see near to even above normal temperatures due to the increased influence of Pacific air across those regions. 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: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Feb 17-Feb 18. - Much below normal temperatures for parts of mainland Alaska, Fri-Mon, Feb 14-Feb 17. 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