Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 516 PM EST Mon Dec 02 2019 Valid 12Z Fri Dec 06 2019 - 12Z Tue Dec 10 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/ECMWF ensembles are reasonably well clustered and seem to offer above normal predictability and continuity for an active and highly stormy Alaskan weather period Friday through the weekend. A blended composite solution along with the National Blend of Models provides a good forecast starting point. Deterministic model forecast spread and uncertainty increases rapidly by next week, lending a quick transition to a much more compatable ensemble mean blended forecast approach. ...Weather/Hazard Highlights... Mid-upper ridging from northeast Russia to the Arctic will favor deep mean closed Bering Sea troughing aloft. This will support development and reformation of several deep and stormy surface systems over the southern Bering Sea late week and 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 after a couple cold nights late this week. The deep lows offshore will remain a signifciant 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 highlight the west side of Cook Inlet and southeast-facing areas of Kodiak Island and especially the Kenai peninsula where 5-10" of liquid-equivalent QPF is depicted (even a bit higher in the GFS/ECMWF). This activity will be fueled by long fetch and slow to translate plumes of deep lower latitude originated moisture. 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 precipitation for parts of the Alaska Panhandle and mainland Alaska, Sat-Mon, Dec 7-Dec 9. - High winds for parts 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