Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 604 PM EST Wed Dec 21 2022 Valid 12Z Sun Dec 25 2022 - 12Z Thu Dec 29 2022 ...Cold air in place and moist return flow could cause heavy snow across the Panhandle over the Christmas weekend, which will spread west with coastal rain possible into early next week... ...Overview... A strong and persistent upper level high and associated ridging will remain nearly stationary across Siberia through the holiday week. Meanwhile, upper level energy over northeastern Alaska/northern Yukon Christmas morning will retrograde southwestward into a strengthening upper level low over the southern Bering, the latter of which will be in the eastern Bering between the Pribilofs and the Eastern Aleutians. The low will remain nearly stationary, peaking in intensity on Monday. It will act as the center point of a wheel, where "spokes" of Pacific energy race eastward across the North Pacific to the south of the low, then turn north into the Gulf of Alaska. This will remain the pattern right through the extended period, through Thursday morning. This pattern will result in an unsettled and increasingly warmer pattern across much of mainland Alaska, as each North Pacific storm brings a renewed round of precipitation, and warmer air with each round. Thus, the extreme cold over the state will gradually abate through the upcoming holiday workweek. From Christmas into Monday, the first storm of this period will barrel into the Panhandle, resulting in heavy snow. Subsequent storms will gradually track further and further west, resulting in more warm air moving into the Panhandle and southern Alaska. This in turn will make precipitation type increasingly uncertain, at least at the coast. Generally speaking the longer the pattern remains stuck, the less energetic each iteration of storms becomes, so there should be fewer impacts with time as well. For interior and northern Alaska, expect continued cold temperatures as lows continue to dip to near 40 below. These extreme temperatures will also moderate with time, more so due to residual cloud cover from the storms hammering the coast than to any warmer air masses moving in. Nonetheless these temperatures remain well below normal, just not quite as cold as the air mass currently impacting the area. ...Guidance/Predictability Assessment and Preferences... The larger scale upper level pattern through the medium-range continues to be in fair agreement. There is somewhat less retrograding of the upper level low today as compared with 24 hours ago, in favor of an anchoring upper low that remains largely stationary...though certainly not without some wobbling during this time frame. This pattern is a common one in the winter, as compared with a progressively retrograding low...as it allows for a consistent storm track of storms south of the low, that then curl into the Gulf. Further the even more persistent upper high over Siberia is also very common, resulting in a blocking pattern. While confidence has increased on the general consensus of the upper level pattern, the details of storm track and any wobbling of the upper level low remain very uncertain. Due to this, the areas that may see the greatest impacts remain in doubt, so only broad phrasing of warming temperatures and very unsettled conditions across the Gulf are all that can be said with certainty. The GEFS/ECENS were the root models used in the blend for this time frame. The UKMET and CMC both have patterns closer to yesterday, resulting in a less stationary pattern with more retrogression of the upper level low. These are outliers compared with the GEFS & ECENS, which are generally closer with one another and more consistent. As usual, more deterministic models...GFS/EC/UKMET were favored early in the time frame, roughly for days 4,5...blending to much more of an ensemble approach by later in the period as uncertainties with the many North Pacific lows amplify by midweek. ...Weather/Hazards Highlights... Much below normal temperatures are expected to continue across east-central portions of Alaska through Monday. Temperatures could fall into the 30s and 40s below zero in some locations. Ridging, persistent Pacific onshore flow, and plentiful cloud cover should all work to bring temperatures above normal by midweek across the Panhandle, and much closer to normal across Southcentral and the Interior. Heavy snow remains a threat through the Christmas weekend across the Panhandle, with heavy rain/snow mix at the coast/interior Southcentral respectively for Christmas Day and Monday. As mentioned above this is the result of several Pacific storm systems bringing plentiful moisture into a very cold air mass that is currently in place and will be slow to be dislodged/moderate. Wegman Hazards: - Heavy snow across much of the Alaska Panhandle, Sat-Sun, Dec 24-Dec 25. - Much below normal temperatures across portions of mainland Alaska, Sat-Mon, Dec 24-Dec 26. - Heavy precipitation across portions of the Alaska Panhandle and Southcentral Alaska, Sun-Mon, Dec 25-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