Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 332 PM EDT Mon Apr 29 2019 Valid 12Z Fri May 03 2019 - 12Z Tue May 07 2019 The large scale pattern across Alaska will remain relatively unchanged through the extended forecast period. A mean trough will slowly progress eastward across the Aleutians through the period, 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. One significant question that remains is whether shortwave energy will be able to periodically break down the northern extent of the Gulf ridge (as shown by the ECMWF/CMC and to a lesser extent the FV3), or whether the ridge will hold strong (as shown by the GFS). Teleconnections associated with some of the stronger hemispheric 500 hPa height anomalies do not show strong support for the Gulf ridge, leading to the conclusion that at least a temporary/periodic weakening of the ridge northern extent seems feasible. The 00Z ECMWF and 06Z FV3 also showed similar evolution/progression of the upper low slowly moving east across the Aleutians and into the southern Bering Sea from Sat onward, and the associated surface low pressure system. Thus, the forecast during days 4-5 (Fri-Sat) was based heavily on a blend of the ECMWF and FV3 (more weight placed toward the ECMWF), with gradually increasing weight placed on ECENS/NAEFS ensemble means through time, and majority ensemble weighting after day 6 (Sun). 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