Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 746 PM EDT Tue Sep 15 2020 Valid 12Z Sat Sep 19 2020 - 12Z Wed Sep 23 2020 ...Overview and Guidance/Predictability Assessment... The mean pattern will generally be troughy for much of the Alaska region during the extended periods, especially between 160W and 170W, with multiple waves moving through. The first lifts northeast into Canada on Friday, while the next quickly dives from the Bering Sea, across the Aleutians and into the Gulf this weekend. The third system deepens, becoming well-defined and wrapped up as it tracks toward/over the Aleutians mid-to-late in the forecast period. Stronger winds and additional focused rain will accompany this system. High winds may impacts part of Kodiak Island and areas to the west and south Monday and Tuesday. Heavy precipitation spanning Unimak Island to Glacier Bay also possible early next week. While there is some spread in timing and strength, there was been decent consensus the last few runs. Continue to prefer a blend of 12Z ECWMF/GFS/CMC for most periods- with a little inclusion of of the 12Z UKMET initially for the evolution of the leading system and introduced light weighting of the 00Z EC ensemble and 12Z GEFS mean Monday and Tuesday. ...Weather/Threats Highlights... Showers are expected across the southern coastal area with some local enhancement after the lead low pressure system passes through. A majority of the Interior will have daily temperatures near average, or above, for mid-September. However, the clouds and showers will keep much of the southern coastal areas below average, as well as, portions of the North Slope. Another round of rainfall is expected to pass over the Aleutians and into the Alaska Peninsula by late this weekend through midweek as a deepening, low tracks toward the Aleutians. Campbell 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 precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri, Sep 18. - Heavy precipitation across portions of mainland Alaska and the Aleutians, Mon-Tue, Sep 21-Sep 22. - Heavy rain across portions of the Alaska Panhandle, Sun, Sep 20 and Tue, Sep 22. - High winds across portions of mainland Alaska, Mon-Tue, Sep 21-Sep 22. 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