Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EST Wed Dec 16 2020 Valid 12Z Sun Dec 20 2020 - 12Z Thu Dec 24 2020 ...Guidance and Uncertainty Assessment... In general, model guidance continues to produce a low confidence forecast for much of the extend period; however, there is consensus for high pressure setting out over the Arctic and a mean trough with one or more waves to move through the Bering Sea and Aleutians during this time. The upper-level jet will be very strong as it tracks over the North Pacific. A deep storm is progged to move into the Aleutians and Bering Sea, likely to generate a broad area of enhanced precipitation and strong winds, spreading from the western Aleutians on Sun and continuing eastward toward/into the southern and western mainland during the first half of next week. There has been persistent height falls to retrograde into the mainland during the weekend around the periphery of a slowly retreating upper ridge/high. Uncertainties within the weakness aloft and for impulses in Pacific flow keep confidence in the lower half of the range for individual Bering Sea and Gulf of Alaska/northeastern Pacific surface lows. The CMC/GFS/ECWMF had deeper surface lows with this feature and were fairly clustered, at least initially, and was the starting point for the extended forecast. As the storm progressed through the weekend and into early next week, the spread greatly increased and the means had increasing weighting-- more than 50% by midweek. ...Weather/Hazards Highlights... Areas along the southern coast and the Panhandle could have moderate to heavy precipitation through the weekend before letting up some early next week. Locations to the north/Interior will mainly be dry this weekend prior to the arrival of a deep storm system. This system will move through the Aleutians and Bering Sea; likely bringing its leading significant precipitation and brisk to strong winds into the western Aleutians Sunday- advancing through the eastern Aleutians and Alaska Peninsula by Monday, southern/western mainland by Tuesday with moisture possibly as far east as the Panhandle by Wednesday. One or more frontal waves could provide some added focus for winds and precipitation between the eastern Aleutians and southern coast of the mainland. Maximum temperatures across portions of the Mainland are expected to fall below/much below average this weekend; whereas, Southeast Alaska and extreme southeast portions of the Mainland will likely climb above seasonal averages for later December. There wills be an abrupt warming trend next week with much of the region observing above/well above normal temperatures. Campbell Hazards: - Heavy precipitation across the Alaska Peninsula, Mon, Dec 21. - Heavy precipitation across portions of southern Alaska, Tue-Wed, Dec 22-Dec 23. - Heavy precipitation across portions of the Alaska Panhandle into southern Alaska, Wed, Dec 23. - Heavy snow across the eastern portion of the Alaska Panhandle, Sat, Dec 19. - High winds across the Alaska Peninsula into southern Alaska, Mon-Tue, Dec 21-Dec 22. - Much below normal temperatures across much of the lower elevations of eastern Alaska, Sat-Tue, Dec 19-Dec 22. 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 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