Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 635 PM EST Wed Dec 29 2021 Valid 12Z Sun Jan 02 2022 - 12Z Thu Jan 06 2022 ...Overview... The best guidance cluster maintains fairly good continuity with the overall forecast. Early in the week consensus shows a sharp and amplifying upper ridge over the Bering Sea through eastern Siberia and beyond while a deep-layer low drifts southeastward over the Northeast Pacific. There is improving agreement that the ridge should ultimately close off an upper high that drifts over/near or a little northeast of eastern Siberia by midweek while energy retrogrades to some degree south of the closed high. Surface high pressure crossing the northern mainland and settling into eastern Canada will bring a period of cold temperatures to the state while precipitation will tend to be confined to the western two-thirds of the Aleutians in association with one or more waves and then Kodiak Island/parts of the Alaska Peninsula as easterly low level flow develops. ...Guidance Evaluation and Preferences... Recent stronger trends for the upper ridge/high in the ensemble means, as seen in the 12Z CMCens initially and then the 12Z ECMWF mean after forecast preparation, have continued support for emphasizing operational guidance to maintain reasonable strength of the feature through the end of the forecast. Not surprisingly the GFS/ECMWF/CMC runs are shuffling around with respect to the upper high's center by the latter half of the period with an intermediate solution providing a good starting point. Model/ensemble signals have been incrementally increasing confidence in the overall upper high scenario but what happens with energy underneath the high (its shape, degree of retrogression, and latitude) has much lower confidence/predictability. Today's forecast started with a 12Z operational model blend early and then transitioned to splitting ECMWF/GFS input among their last two runs (12Z/00Z for the former and 12Z/06Z for the latter) while keeping the 12Z CMC component. This approach provided the desired average position for the eventual upper high, shifting a bit west of yesterday's forecast as of early day 7 Wednesday, and helped to smooth out the very uncertain details of the developing elongated upper weakness to the south. The blend also helped to maintain definition of the strong high pressure crossing the northern mainland as well as the tight gradients/strong winds over the southern mainland and Panhandle through the forecast plus over the western half or so of the Aleutians early in the period. ...Weather/Hazard Highlights... Expect precipitation over the Panhandle to trend lighter on Sunday with continued drying thereafter as Northeast Pacific low pressure drifts southeastward and becomes gradually weaker. Much of the mainland will see dry conditions Sunday-Thursday. The western half or so of the Aleutians will likely see a period of organized/enhanced precipitation and strong winds from late weekend into the early part of next week as one or more waves track around the western periphery of the building upper ridge. Some locations from Kodiak Island and the Alaska Peninsula westward may see precipitation develop as low level easterly flow sets up but confidence in specifics is low at this time. High pressure crossing the northern half of the state early in the week will bring well below normal temperatures especially into southern and eastern areas from west to east. The coldest anomalies should start to moderate by midweek while temperatures over the northern mainland should trend increasingly above normal. The strong gradient between high pressure (possibly exceeding 1050mb for a time) and the northeastern Pacific low should produce a period of strong winds across the southern mainland and Panhandle. Rausch Hazards: - Heavy snow across portions of the Alaska Panhandle and mainland Alaska, Sat, Jan 1. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sat-Mon, Jan 1-Jan 3. - High winds across portions of the Aleutians, Mon, Jan 3. - Much below normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Sun-Wed, Jan 2-Jan 5. 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