Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun Apr 14 2019 Valid 12Z Thu Apr 18 2019 - 12Z Mon Apr 22 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, especially during the second half of the forecast period. Model consensus has gradually improved that a relatively deep low pressure system should move north into the Gulf of Alaska by Thu. For several runs models had shown some variability between taking the low more farther east closer to the Alaska Panhandle, or farther west toward southern mainland Alaska. Solutions seem to be settling more toward the western solutions, with the last holdout (GEM global) coming on board with the 12Z run. This system appears likely to produce an episode of widespread and potentially heavy precipitation, along with gusty winds, for portions of the Alaska Panhandle on Thu. In the wake of this low pressure system, predictability gradually decreases through time. Model consensus has improved a bit around an arctic shortwave progged to dive south across the eastern Bering Sea late Fri into Sat, with potential interactions with energy crossing the north Pacific during that time. A second arctic shortwave following a similar track late Sat into Sun shows increased spread over the leading wave. 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. While spread has perhaps reduced a bit compared to 24 hours ago, models still vary widely on the timing and intensity of this system. Given these considerations, the forecast during days 4-5 (Thu-Fri) was based heavily on a blend of the 00Z ECMWF/12Z GFS. After Fri, weighting of ECENS/GEFS ensemble means was gradually increased through time to account for increasing spread/decreasing predictability. 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