Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 602 PM EDT Mon Sep 07 2020 Valid 12Z Fri Sep 11 2020 - 12Z Tue Sep 15 2020 ...Potent Weekend Storm for the Aleutians then Southwest to Southern Alaska early next week... ...Weather/Threats Highlights and Guidance/Predictability Assessment... A potent weekend storm is slated reach the southern Bering Sea/Aleutians with ample energy from a northern stream closed upper trough/low as well as tropical influences. There is a growing signal for deep low development as enhanced by an infusion of energy/moisture with the extratropical evolution of former Super Typhoon Haishen. This leads to a threat of high winds/waves and heavy rains for the Bering Sea/Aleutians to then spread into southwest/AKpen and southern Alaska into early next week. Models and ensembles offer a reasonably similar larger scale pattern evolution aloft, but still differ with embedded system details and continuity, especially at the complex surface, for the storm as well as for a separate Arctic stream flow. The Arctic flow is more benign, but does feature some cooling frontal push to an unsettled North Slope/Interior this week underneath an amplified Arctic closed low/trough. The WPC Alaskan medium range product suite was primarily derived from a composite blend of the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble means days 4-8. The GFS/ECMWF were highly weighted in this blend only Day4/Friday, transitioning preferences quickly in favor of the more consistent/compatible ensemble means and the 19 UTC National Blend of Models thereafter in a period of growing forecast spread. Manually adjustments to the blend were applied to ensure sufficient storm depth consistent with the tropical history of the system and expected favorable upper support. 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 for parts of the Alaska Panhandle, mainland Alaska, and Aleutians, Sun-Mon, Sep 13-Sep 14. - High winds across portions of mainland Alaska and the Aleutians, Sun-Mon, Sep 13-Sep 14. 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