Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 706 PM EST Tue Dec 06 2022 Valid 12Z Sun Dec 11 2022 - 12Z Thu Dec 15 2022 ...Overview... The ensemble means have been fairly persistent with portraying a series of upper-level features of moderate progression and amplitude through the extended period. Individual deterministic model solutions have varied significantly the past few days and both the ensemble means and their parent models have had a lot of run-to-run variability and/or trending for embedded features. This is particularly the case for one or more systems that could affect areas from the Aleutians through the western/southern mainland, but also applies to specifics within a general signal for increased storminess over and possibly east/north of the northwestern Pacific by early next week. Although there continues to be variance with the ridge axis location, this feature has the most confidence through the extended forecast. With it progged to settle in over the eastern part of the state and into western Canada, colder air will reside over portion of the Southeast and eastern Mainland later in the period. ...Guidance/Predictability Assessment and Preferences... Initial smaller-medium scale systems involve a wave/frontal system over the Bering Sea/Aleutians, low pressure that may track along the northwest coast of the Bering Sea, and low pressure off the southeastern coast/Panhandle. Finally, low-predictability shortwave details will have a say in the details of low pressure initially over or near the Gulf of Alaska. The latest runs of the guidance continue to show a large degree of spread in amplitude, location and progression with several features but most notable is the system that should reach south of the Aleutians by early Saturday. For early next week the guidance has offered a general signal for one or more significant surface lows within an area from the northwestern Pacific into the Aleutians and western Bering Sea. 12Z model trends have been toward slower overall progress of strongest low pressure relative to the means. The WPC preferred blend began with a general consensus of the ECWMF/CMC/UKMET/GFS. Beyond Day 4 the inclusion of the ensemble mean increased (while dropping the UKMET and reducing the weighting of the ECWMF, GFS and CMC); reaching approximately 30-50% by Day 5/6 and 50-70% means by Day 7/8. This approach maintains the conservative approach while maintaining WPC forecast continuity. ...Weather/Hazards Highlights... The most confident part of the forecast appears to be with the establishment of well below normal temperatures over southern/eastern areas as surface high pressure settles over portions of the mainland into western Canada. In contrast, a majority of the northwest half of the state is expected to maintain above normal temperatures, or moderate toward normal through the end of the forecast period. This gradient of surface pressure will likely lead to the presence of locally strong gap winds over the Gulf of Alaska/northeastern Pacific Ocean this weekend onward along the southern coast and Panhandle. Guidance is still resolving important details for North Pacific low pressure that may affect the Aleutians and potentially parts of the western/southern mainland during the weekend into early next week. Model trends have been increasing the potential for some areas to see meaningful precipitation and some brisk to strong winds, especially along the southern portion of the state. Some moisture could eventually reach as far east as the Panhandle. Most of the solutions indicate daily amounts of 1 to 2+ inches as it skirts eastward, however a couple are hinting the 3 to 7+ may impact portions of the Kenai Peninsula, Kodiak Island and the southern Coast. There are also question marks about the eastward influence of a system that may track well west of the northwestern mainland, with some potential (though for now in the minority) for a brief period of increased precipitation and wind. Finally, another system may affect some areas over the Aleutians and Bering Sea early next week with enhanced precipitation and wind but again the specifics are very uncertain at this time. Campbell/Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Mon, Dec 12. - High winds across portions of mainland Alaska, Sun, Dec 11. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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