Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 731 PM EDT Fri Aug 28 2020 Valid 12Z Tue Sep 01 2020 - 12Z Sat Sep 05 2020 ...Guidance/Predictability Assessment... The WPC Alaskan medium range products suite was primarily derived from a composite blend of well clustered guidance from the 12 UTC GFS/ECMWF/UKMET valid Tuesday through Thursday (Days 4-6). This solution also has broad ensemble support. Forecast spread is relatively low in this period, but predictability seems no better than average considering run to run embedded system variances recently in progressive flow during this period. The 12 UTC ECMWF then seems the best fit with GEFS/NAEFS/ECMWF ensemble means and WPC continuity into days 7/8 during a period of rapid flow amplification. ...Weather Highlights/Threats... A potent upper jet will punch over the northern Pacific to the Gulf of Alaska. Early week energy transfer and a deep tropical moisture plume associated with former west Pacific Typhoon Bavi will favor lingering enhanced precipitation into southeast Alaska into Tuesday, especially for favored terrain. Several less defined systems in this active flow and out from the southern Bering Sea that will locally focus adverse weather are proving difficult to properly time at medium range time scales. Meanwhile overtop, there is an uncertain focus with individual systems slated to work into an amplified Bering Sea/Strait to western Interior mean upper trough position next week. However, predictability is high that the cooling and unsettling pattern will persist next week, albeit with an increasing focus over the Bering Sea through the period with flow amplification. A guidance trend toward rapid flow amplification days 6-8 overall itself seems quite reasonable. It seems well supported by the forecast track of developing far western Pacific Typhoon Maysak northward to northeast Asia over the next week. This should act to build downstream upper ridging over the northwest Pacific and an amplified upper trough down through the Aleutians, setting the stage for a renewed low/storm development and focused enhanced weather threat. 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 Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon, Aug 31. - Heavy rain across portions of the Alaska Panhandle, Mon-Tue, Aug 31-Sep 1. 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