Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 520 PM EST Thu Dec 16 2021 Valid 12Z Mon Dec 20 2021 - 12Z Fri Dec 24 2021 ...Overview... The main theme going into next week will be a dominant upper ridge/surface high pressure over the North Pacific with multiple shortwaves/storm systems tracking around the northern periphery of the high. A slow moving polar low near 75 degrees north is also expected to remain in place for much of next week. A strong cold front is expected to cross most of the state early in the week and bring a return to colder temperatures after above average readings on Monday. ...Guidance Evaluation and Preferences... The 12Z model guidance suite is in good overall agreement on Monday across the Alaska domain. The upper high centered south of the Alaska Peninsula has the greatest model agreement through the extended forecast period, and the polar low north of the Arctic Coast is also well represented by the guidance. Model differences become apparent with shortwave energy crossing the Aleutians and northern Gulf, and the UKMET in particular stands out from the consensus by Monday night and into Tuesday with a much faster and stronger trough over the northern Gulf of Alaska that is not favored by the ensemble means. The 12Z GFS is also quite strong with this same feature, but closer in timing with the weaker CMC/ECMWF solutions. Model differences continue for the next system to cross over southern Alaska/Gulf region by Thursday, and the CMC differs more so with a considerably stronger ridge axis extending north into the Interior, with the incoming trough quite a bit slower. Taking these factors into account, the WPC forecast is primarily derived from a CMC/GFS/ECMWF/ensemble mean blend through Wednesday, and then ECMWF/some GFS/increased ensemble means for next Thursday and Friday. ...Weather/Hazard Highlights... Precipitation, mainly in the form of snow, is likely for western and central parts of the mainland through early Tuesday, given the increasing deep layer moist southwesterly flow into the state to the west of the Pacific ridge. From the Brooks Range southward into parts of western and central Alaska, snow may be heavy over terrain favored by strong southwesterly winds on Monday. Strong low level winds are expected, which along the coast may even lead to areas of coastal flooding. Areas with a combination of snow and strong winds could see blizzard conditions. Another round of precipitation may affect the Aleutians and southwestern Alaska around next Wednesday-Thursday as another Pacific storm system approaches. Temperatures are expected to be pleasant for this time of year and thus well above average across much of the mainland to begin the week, with the potential for some daily record highs to be established. Some inland locations that have been below freezing for many weeks might get readings above 32 degrees briefly early in the week before reality sets in after a strong cold front moves through. Hamrick 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 Hazards: - Heavy snow across portions of mainland Alaska, Sun, Dec 19. - Heavy snow across portions of mainland Alaska, Sun-Mon, Dec 19-Dec 20. - Heavy snow across portions of mainland Alaska, Mon, Dec 20. - High winds across portions of mainland Alaska and the Aleutians, Sun, Dec 19. - High winds across portions of mainland Alaska, Sun-Mon, Dec 19-Dec 20. - High winds across portions of mainland Alaska, Tue-Wed, Dec 21-Dec 22. 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