Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 640 PM EDT Sun May 09 2021 Valid 12Z Thu May 13 2021 - 12Z Mon May 17 2021 ...Guidance/Predictability Assessment... Latest 12 UTC GFS/ECMWF/Canadian model solutions seem reasonably well clustered and consistent days 4-6 (Thu-Sat) and enjoy ample ensemble support. A composite blend seems to produce a good forecast starting point consistent with a pattern with above normal predictability and maintains great WPC product continuity. The ECMWF/Canadian and to a lesser extent ECMWF ensemble solutions remain best clustered into day 7/8 and bring a much deeper low into the Aleutians day 7/8 than the GFS. The GFS does not match well with GEFS ensembles either at these longer time frames, lowering forecast confidence. Used a composite blend of the 12 UTC ECMWF/Canadian and ECMWF ensemble mean to show a reasonably deep low as there seems to be an established/dynamic storm pattern out from eastern Asia. ...Weather/Threats Highlights... Upper trough energies and lead/complex precipitation focusing surface lows/frontal weather systems will work across the Gulf of Alaska to southern/southeastern Alaska into later this week, undercutting a warming and stabilizing interior upper ridge. Meanwhile upstream, amplified/closed upper trough energy is slated to track over the southern Bering Sea/Aleutians and deepening low pressure will support increasingly unsettled maritime conditions and inland feeding enhanced rains and winds across the region. Activity is expected to translate downstream into Southwest Alaska, the Alaskan Peninsula, Kodiak Island, the Gulf of Alaska, the southern interior and then southern and southeast Alaska through next weekend with steady main system progression and lead triple point low developments and inflow. A less certain second main low with enhanced rains/winds may reach the Aleutians next Sun/Mon. Schichtel 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 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