Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 601 PM EST Tue Dec 03 2019 Valid 12Z Sat Dec 07 2019 - 12Z Wed Dec 11 2019 ...Deep Lows lend a Maritime Hazard and Southern AK Tier Heavy Precipitation Threat... ...Guidance/Uncertainty Assessment... The 12 UTC GFS/ECMWF and 12 UTC GEFS/NAEFS/ECMWF ensembles are reasonably well clustered Saturday-Sunday and seem to offer above normal predictability and continuity for a stormy Alaskan weather period. A blended approach (with more weighting on the deterministics) provides a good forecast starting point. Deterministic model forecast spread and uncertainty increases rapidly by next week, particularly regarding timing/placement/intensity of various surface low developments towards the Aleutians/Gulf of Alaska early next week. This lends to a transition towards more weighting on the better clustered ensemble means with smaller contributions from the deterministic runs just for some definition. ...Weather/Hazard highlights... Mid-upper ridging from northeast Russia to the Arctic will favor deep mean closed Bering Sea troughing. This will support development and reformation of several deep and stormy surface systems over the southern Bering Sea through the weekend. Slow movement favors locally heavy rain/snow downstream whose forcing mechanisms should prove slow to progress eastward, but eventually work across the Gulf of AK to the Southeast Panhandle early next week with pattern transition. Meanwhile overtop in the interior, high pressure will slowly shift into Canada this weekend. Deep lows offshore will remain a significant maritime hazard to include high winds and waves. Multiple periods of heavy precipitation will also work onshore and focus over the AKPEN/Southwest AK heading into the weekend and then expand across Southcentral then Southeast AK where it could be locally heavy (coastal rain, inland/terrain snow). This transition occurs into next week as triple point developments focus near Kodiak Island. Ensemble QPF guidance highlights much of the south side of the AKPEN to coastal regions of the Prince William Sound (including Kodiak Island) where 5-10" (or more) of liquid-equivalent QPF is depicted. This activity will be fueled by long fetch and slow to translate plumes of deep lower latitude originated moisture. Santorelli 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, Sat-Sun, Dec 7-Dec 8. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Dec 7-Dec 8. 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