Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 635 PM EST Fri Dec 11 2020 Valid 12Z Tue Dec 15 2020 - 12Z Sat Dec 19 2020 ...Guidance and Uncertainty Assessment... Models and ensembles are similar for the broad pattern evolution but suggest low confidence/predictability for a lot of the details that may be important over some areas. Consensus shows a strong upper ridge/high over the Arctic while progressive flow prevails over the Pacific. Between the ridge and Pacific flow there will be a broad weakness aloft likely to extend from Kamchatka through the Bering Sea, Mainland Alaska, and into northern Canada. One of the more agreeable upper lows within this weakness seems most likely to drift near Kamchatka into the western Bering while another meanders over northern Canada. Other upper lows may form as well, such as over or near the northern/eastern Bering Sea as some guidance has been suggesting toward late next week. Low-predictability specifics of individual Pacific shortwaves and possible interaction with features embedded within the broad east-west weakness aloft (which have their own uncertainties) lead to below average confidence in resolving surface low/front details for most of the period. Early in the period there is some degree of clustering on a concentrated surface low that may track near or just north of Haida Gwaii (12Z GFS a bit on the strong/northeast side of the spread) while a wave initially over the Aleutians lifts into the Bering Sea. A modest shortwave continuing eastward from over/south of the southwestern mainland/Alaska Peninsula may produce a short-lived system over the Gulf of Alaska by early Wed. Due to a delay in model data, the 12Z ECMWF was not available in time for preparation of today's 500mb and surface forecast. A blend among the 12Z GFS-CMC-UKMET/00Z ECMWF reflected the most common ideas of guidance and offered some improved detail over the means. After Wed individual models/consecutive runs essentially devolve into a random assortment of various surface lows over the North Pacific/Gulf/Bering. There is a general signal that low pressure may try to consolidate over or near the Gulf toward next Fri or Sat. Lack of model agreement for specifics favored a transition toward greater 12Z GEFS/00Z ECMWF mean input late in the period. ...Weather/Hazards Highlights... Expect windy conditions over portions of the Interior next week, with the mainland in the gradient between strong Arctic high pressure and various low centers over the Bering Sea and Gulf of Alaska. Most precipitation during the period should be confined to locations from the Aleutians through the far southern mainland and Panhandle. Intensity/timing/coverage details are difficult to resolve at this time, though guidance is generally signaling some increase in precipitation over the southern coast and Panhandle by late next week/early weekend as low pressure consolidates over the Gulf. Other systems/fronts may provide one or more episodes of focused activity over the Aleutians/Peninsula. Below to well below normal temperatures will become more widespread with time over a majority of the state as heights within the east-west weakness aloft trend lower. Offshore surface low will likely keep temperatures below normal over southern areas and the Panhandle/eastern Interior as well. Rausch Hazards: - High winds across portions of mainland Alaska, Mon-Tue, Dec 14-Dec 15. - Much below normal temperatures across portions of mainland Alaska, Wed-Fri, Dec 16-Dec 18. 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