Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 337 PM EDT Sat Apr 13 2019 Valid 12Z Wed Apr 17 2019 - 12Z Sun Apr 21 2019 Models/ensembles show broad consensus that upper ridging should persist/expand across eastern Russia and the western Bering Sea during the extended forecast period. A strong jet across the north Pacific will undercut the ridge with a stream of shortwave energy feeding into and reinforcing a mean upper-level trough extending from mainland Alaska south into the Gulf of Alaska. Shortwave energy spilling over the crest of the ridge will also move south across the eastern Bering Sea throughout the period, interacting with the mean trough as well as energy from the north Pacific, introducing an additional degree of complexity/chaos to the forecast and reducing predictability, particularly by the second half the forecast period. Models show some consensus that a potentially deep low pressure system should move north into the Gulf of Alaska Wed-Thu, but solutions differ on the exact track that the system will take. The 00Z ECMWF and 06Z/12Z runs of the GFS showed relatively good consistency in taking the low to near the Kenai Peninsula by late Thu, but the 12Z ECMWF shifted farther east, keeping the low much closer to the Alaska Panhandle. Ensemble spread has generally supported an idea closer to the GFS or previous ECMWF, but confidence remain a bit below average given the continued variability of solutions. Regardless, this system appears likely to produce a period of widespread and potentially heavy precipitation for portions of the Alaska Panhandle late Wed into Thu. In the wake of this low pressure system, predictability decreases quickly through time. Models vary significantly with how to handle arctic shortwave energy diving south across the eastern Bering Sea by Fri-Sat, with potential interactions with energy crossing the north Pacific during that time. Models have varied substantially with a potential low pressure system moving well south of the Aleutians on Sat and its eventual track/evolution as it perhaps approaches the Gulf by Sun. Given these considerations, the forecast during days 4-5 (Wed-Thu) was based heavily on a blend of the 00Z ECMWF and 06Z/12Z GFS runs. After Thu, weighting of ECENS/GEFS ensemble means was boosted substantially given the quickly increasing uncertainty. Ryan Bullet points from the WPC Days 3-7 Hazards chart can be found at: https://www.wpc.ncep.noaa.gov/threats/threats.php 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