Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 539 PM EST Mon Nov 16 2020 Valid 12Z Fri Nov 20 2020 - 12Z Tue Nov 24 2020 ...Deep late week lows to threaten Southwest/Southern Alaska... ...Guidance/Predictability Assessment... The WPC Alaskan medium range product suite was primarily derived from a composite blend of the reasonably compatible 12 UTC GFS/ECMWF, the 12 UTC GEFS mean and the 19 UTC National Blend of Models days 4-6 (Fri-Sun) in a pattern with average to above average system predictability. Used a mass field solution close to the 12 UTC GEFS mean days 7-8 amid quickly growing forecast uncertainty, but manually adjusted offshore lows deeper consistent with favorable upper support and model trends. The 00 UTC ECMWF was an unusual outlier days 7/8, but the 12 UTC run has trended toward the 12 UTC GEFS mean in a pattern with below normal predictability. ...Weather/Threats Highlights... There remains a strong guidance signal supporting amplified upper trough/closed low developments into the Bering Sea and Aleutians into late week, with additional reinforcements into early next week. These will offer several significant threats for deep offshore storms to focus enhanced winds/waves and precipitation across the region. Downstream energy transfer later week through early next week will also increasingly threaten southwest Alaska, southern Alaska, then southeast Alaska as ample upper trough/deepened storm energies work more in earnest into and across the Gulf of Alaska. Schichtel Hazards: - Heavy precipitation across portions of mainland Alaska and the Aleutians, Fri, Nov 20. - High winds across portions of mainland Alaska and the Aleutians, Fri, Nov 20. 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