Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 643 PM EST Thu Dec 22 2022 Valid 12Z Mon Dec 26 2022 - 12Z Fri Dec 30 2022 ...Cold air in place and moist return flow could cause heavy snow across the Panhandle through Christmas Day, which will spread west with coastal rain possible into early next week... ...Overview... The final workweek of 2022 will start out with an upper level low over the western Bering, near Adak. The low will be nearly stationary south of a retreating upper level high over Siberia. Once the high allows the cutoff low to open up into an amplified upper level trough, it will weaken as it begins to move east across the Bering to the coast of Southwest Alaska by next Friday. While the low sits nearly stationary through Wednesday, several shortwaves will rotate around the low, being invigorated by a strong North Pacific jet. These shortwaves will intensify a series of North Pacific lows as they move south of the low and the Aleutians and into the Gulf. This upper level pattern features the main upper level cutoff low being displaced several hundred miles to the west of the forecast from yesterday. The effects of this change are not overly dramatic...instead of the surface lows turning quickly from an eastbound track to a northbound one into the Gulf, instead those lows will simply move east-northeastward past the Aleutians and Kodiak Island into the Gulf. Thus, the pattern continues to remain unsettled for all of the coastal areas of the Gulf. Warmer air and plentiful cloud cover will persist across nearly all of Alaska, so the forecast of moderating temperatures through the workweek also remains unchanged. ...Guidance/Predictability Assessment and Preferences... The larger scale upper level pattern remains only slowly changing, as early on, a semi-Rex block remains in place across the Bering. As mentioned above, the main change was that the primary cutoff upper level low has shifted several hundred miles west of yesterday's forecast, from near Dutch Harbor/Pribilofs to north of Adak. What remains consistent is that there's significant uncertainty, despite the slowly-changing upper level pattern, as to where each North Pacific low will track and the timing of each. Therefore, favoring any one deterministic model results in significant discrepancies, especially in later time periods, with every other model. A plot of surface lows from all of the ensemble members of the ECENS and GFS results in a giant cloud of possible low centers from the Panhandle right through the Aleutians. Given all of this, continuity was the guiding principle for surface features for this time period. The EC deterministic and ensemble blends best represented continuity from yesterday's forecast, even all the way out to next Friday. Thus, these were favored for today's forecast until some semblance of agreement can be attained. ...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. 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 that will be slow to be dislodged/moderate. Wegman Hazards: - Heavy precipitation across the northern Alaska Panhandle and Southcentral Alaska, Sun-Mon, Dec 25-Dec 26. - Heavy snow across the central and southern Alaska Panhandle, Sun, Dec 25. - Much below normal temperatures across portions of eastern interior 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