Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 524 PM EST Tue Dec 21 2021 Valid 12Z Sat Dec 25 2021 - 12Z Wed Dec 29 2021 ...Overview... The extended range forecast over Alaska through the middle of next week will continue to be dominated by a blocky and anomalously strong upper level ridge and surface high pressure over the northeast Pacific. Multiple shortwaves/storm systems are expected to track around the western and northern periphery of the high, but nothing strong enough to break it down significantly through the period. Periods of light snow will be possible across portions of Western Alaska as these systems weaken as they track inland. ...Overview and Guidance Evaluation... The 12Z model guidance suite remains in excellent overall agreement on the large and in charge surface/upper level high centered over the North Pacific near 45N/155W through the entire forecast period, with perhaps a slightly southward budge by early next week. The models also strongly suggest a north-south oriented ridge axis should exist across western mainland Alaska. The main model differences reside across the Aleutians and the Bering with the storm system tracking towards the northeast in the general direction of northwestern Alaska. The strongest signal for a shortwave will be on Sunday/early Monday across the northern half of the state as it traverses the northern periphery of the ridge, with the GFS/CMC indicating a stronger signal. A second storm approaching the western Aleutians has a greater model spread, with the 12Z ECMWF much stronger across the Bering by next Tuesday night and loses ensemble support. Taking these factors into account, a general deterministic 12Z model blend should suffice as a starting point through the upcoming weekend, followed by slightly more of the GFS/CMC than the ECMWF and increased use of the ensemble means. ...Weather/Hazard Highlights... A storm system and associated cold front originating from the Bering and western Aleutians is forecast to move quickly across interior sections of the mainland Sunday. Moisture advection ahead of the front will support patchy areas of moderate to locally heavy snow across the Seward Peninsula, the southern part of the Brooks Range, and eastward toward the Fairbanks area and the central Interior. Some of this snow will likely be accompanied by strong winds, leading to blowing snow and localized blizzard conditions, particularly in mountain passes. Another round of accumulating snow will be possible by next Tuesday depending on the track of the next storm system entering the Bering. In the temperature department, frigid conditions are expected for eastern and northern portions of the mainland this weekend, with a moderating trend commencing by late Sunday and a return to above normal readings by the early to middle part of next week. Hamrick Hazards: - Heavy snow across portions of mainland Alaska, Sun, Dec 26. - High winds across portions of mainland Alaska, Fri, Dec 24. - Much below normal temperatures across portions of the Alaska Panhandle, Fri-Tue, Dec 24-Dec 28. 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