Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 PM EDT Wed May 01 2019 Valid 12Z Sun May 05 2019 - 12Z Thu May 09 2019 The large scale pattern across Alaska will remain relatively unchanged through the extended forecast period. Mean upper troughing is expected to persist across the Bering Sea, with somewhat transient upper ridging centered across the Gulf of Alaska, and a more persistent ridge of high pressure farther north in the Arctic Ocean. This flow pattern results in a constant stream of shortwave energy crossing near/south of the Aleutians and moving into mainland Alaska, with additional shortwave energy rotating around the southern periphery of the arctic ridge affecting the North Slope. The WPC forecast was initially based heavily on the ECMWF/GFS during days 4-5 (Sun-Mon), with gradually increasing weight placed on the ECENS/GEFS ensemble means during days 6-8 (Tue-Thu). The ECMWF/GFS handle the shortwave/upper low crossing the Aleutians, and the weakening of the Gulf ridge, similarly during the Sun-Mon time frame. Farther to the north, differences with respect to arctic energy rotating westward around the southern periphery of the arctic ridge are primarily confined to intensity, so a blend of the two solutions should represent a consensus solution well. The GFS starts to differ quite significantly from day 6 onward, bringing a deep low pressure system into the western Bering Sea, with little additional deterministic or ensemble support. Thus, the GFS was excluded from the forecast blend starting on day 6. The ECMWF is in general agreement with ensemble means that a slowly progressing shortwave and associated occluded/filling low pressure system should cross the Alaska Peninsula during the early-middle portion of next week, perhaps pushing into the interior by Thu as the system quickly weakens. Overall, the forecast was fairly similar to continuity. 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