Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EST Tue Dec 20 2022 Valid 12Z Sat Dec 24 2022 - 12Z Wed Dec 28 2022 ...Cold air in place and moist return flow could lead to heavy snow across the Panhandle late this week... ...Overview... Upper level energy initially over eastern Alaska/northwest Canada on Saturday will slowly retrograde westward across the Mainland Alaska, sandwiched in between a strong upper high over the Arctic and a building and blocky ridge over western Canada. Eventually this energy looks to settle over the Bering Sea or near the Aleutians by the middle of next week. Verious pieces of energy look to rotate around this low south of the Aleutians and into the Gulf through the period. While there is still a lot of uncertainty in the details, the overall idea is that precipitation is likely across the Panhandle this weekend, shifting northward with time towards the south-central coastal region. The main threat should be heavy snow, though some mixing with rain is possible along the immediate coast. ...Guidance/Predictability Assessment and Preferences... There is overall good agreement on the large scale pattern over Alaska, but significant uncertainties in the details particularly pertaining to multiple surface lows well to the south of Alaska, which could eventually lift towards the Gulf. Given this, inclusion of the ensemble means in the forecast blend as early as day 4 seemed pertinent to attempt to tone down the noise in the deterministic guidance. For days 4-6, was able to use a majority (80 percent) blend of the deterministic 12z GFS, ECMWF, and UKMET along with the ensemble means. The CMC was not used during the period as it tended to stray the most from the means with a much slower and more northerly progression of the upper low retrograding over the mainland. After day 6, a nearly 50 percent deterministic GFS/ECMWF and 50 percent ensemble mean blend was used. Though with plenty of differences in the timing and placement, the guidance does show decent agreement for at least a couple of modestly deep lows to approach the Panhandle early next week and near the Aletians by the middle of the week. ...Weather/Hazards Highlights... Much below normal temperatures are expected to continue across especially east-central portions of Alaska but also into central and southwest Alaska too. Temperatures could fall into the -30s and -40s F in some locations. Compared to a cold short range period, ridging building back in near the Panhandle region should allow temperatures to moderate somewhat through the period with above normal temperatures possible again by early next week across the Panhandle and southeast Alaska. Increasing moisture across the Panhandle brings a threat for widespread heavy snowfall, mainly this weekend. Moisture should work its way northward as well in response to an approaching surface low but may mix with rain as temperatures moderate across the southcentral Coast. Some scattered precipitation is likely back into the Peninsula and the Aleutians but the remainder of the AK mainland should be mostly dry through the period. Additionally, a strong pressure gradient setting up between arctic high pressure and northern Pacific low pressure should allow for continued and gusty winds across much of Alaska this weekend and into next week. Santorelli Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Dec 25-Dec 27. - Heavy snow across portions of the Alaska Panhandle, Fri-Mon, Dec 23-Dec 26. - Much below normal temperatures across portions of mainland Alaska, Fri-Mon, Dec 23-Dec 26. 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