Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EST Sat Dec 18 2021 Valid 12Z Wed Dec 22 2021 - 12Z Sun Dec 26 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 and western periphery of the high. This ridge axis builds northward across the Bering and western Alaska by Christmas weekend as a blocking pattern tries to develop. Episodes of light to moderate snow are expected across portions of the mainland. ...Guidance Evaluation and Preferences... Similar to yesterday, models and ensembles are in excellent agreement on the large high over the North Pacific centered near 45N/160W for much of the extended period, with perhaps a slight southward drift by next weekend. The greatest model uncertainties reside with shortwave impulses/surface lows tracking northeastward on the western/northern periphery of the ridge axis, and whether any of these impulses might be able to erode the northern ridge axis over the northern half of Alaska. The CMC solution indicates the best potential for this to happen on Thursday, while the GFS/ECMWF indicate a relatively weak shortwave reaching northwest Alaska by Saturday. Except for a stronger disturbance over far northeast Alaska early in the forecast period, the UKMET is reasonably close to the model consensus. Taking these factors into account, the WPC forecast is primarily derived from a UKMET/GFS/ECMWF/ensemble mean blend through Friday, and then ECMWF/some GFS/increased ensemble means for next weekend. ...Weather/Hazard Highlights... The coldest temperatures during this forecast period are expected to be across the northeast quadrant of the state where light winds and a strong surface inversion are expected to be in place. Periods of mainly light snow are likely across much of the western half of the state associated with warm air advection aloft from the low pressure systems passing over the Bering Sea. Given the strong ridge in place over the Gulf/North Pacific, no areas of heavy precipitation are currently expected for coastal portions of southern Alaska nor the southeast Panhandle region. 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 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