Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 655 PM EST Mon Jan 17 2022 Valid 12Z Fri Jan 21 2022 - 12Z Tue Jan 25 2022 ...Heavy precipitation along the southern coast and Panhandle late week into the weekend, with a wet pattern continuing into next week... ...Overview... Guidance continues to show a very warm and wet pattern as a strong eastern Pacific mean ridge extends northward into Mainland Alaska and northwestern Canada while a mean trough axis persists farther west. Within this trough there should initially be a fairly deep northern Bering Sea upper low that may influence strong low pressure expected to track northward along the western coast of the mainland. Moist flow ahead of this system will focus significant precipitation across the southern/western parts of the state with highest totals likely over the southern coast and Panhandle. Forecast details become more uncertain after the initial system departs and the overall upper trough gradually weakens, but there is a general theme that additional significant precipitation will be possible over some areas between the Alaska Peninsula and Panhandle through next Tuesday. ...Guidance/Uncertainty Assessment... The 12Z operational model consensus has trended faster for the leading system that should track northward near the western coast of the mainland. At the time of forecast preparation, the 12Z GEFS/CMCens supported this trend as well. The new 12Z ECMWF mean has come in close to its operational run. The fast flow aloft between the deep northern Bering upper low and ridge to the east seems to support this adjustment. Remaining forecast details have lower confidence. There is lingering spread and inconsistency with the ultimate path/evolution of the northern Bering upper low and surrounding energy, with some effects on surface evolution across the mainland during the first half of the period. Meanwhile recent GFS runs have been fairly much on their own in bringing stronger shortwave energy and a defined surface wave into the northeastern Pacific/Gulf of Alaska by around Sunday when most other model/mean solutions have this area within the gradient ahead of stronger low pressure farther west. In runs since the 00Z cycle, the 06Z version was the least extreme so the GFS input for the forecast exchanged the 12Z run for the 06Z one by Sunday. As for the aforementioned western system, there is a decent signal for it to approach the eastern Aleutians by Sunday and then track into the southeastern Bering Sea. However there is still a lot of spread for its timing/track/strength as well as for details of yet another potential system that may or may not interact with it. A blend of the 12Z operational models provided a good representation of latest consensus for about the first half of the period, again with GFS input switching to the 06Z version by Sunday due to Northeast Pacific/Gulf issues at that time. The widening spread for details later in the period favored a conservative approach that included splitting ECMWF input between the past two runs after Sunday as well as increasing the total weight of 12Z GEFS/00Z ECMWF mean to 50 percent by day 8 Tuesday. This blend yielded a Monday-Tuesday evolution of the southeastern Bering system quickly weakening in favor of the next system to the south/southeast, but with minimal confidence. ...Weather/Hazard Highlights... Guidance consistently shows the most pronounced surge of moisture reaching the state Friday into Saturday, carried by the strong flow ahead of a storm likely to track northward across the western Alaska Peninsula and near the western coast of the mainland. The atmospheric river event should bring the highest totals to the southern Coast and Panhandle with somewhat greater focus over the Panhandle by Saturday. Operational models continue to depict precipitable water values exceeding three standard deviations above normal over some locations during this episode. Strong winds will be possible as well, and other areas across the western and southern mainland may see brisk to strong winds with terrain-enhanced precipitation. After Saturday the most likely scenario would have precipitation trending lighter over the Panhandle for a time while the next system to the west renews focus of significant precipitation over the Alaska Peninsula and the southern coast, possibly reaching into the Panhandle by next Monday or Tuesday. Some moisture may spread farther north as well. There is a lower potential for a separate wave to prolong heavy activity over the Panhandle into Sunday before a lighter trend. The Aleutians will likely see episodes of organized precipitation and at least brisk winds with individual systems but with lower than desired confidence in specifics. To start the period on Friday, the North Slope and far western parts of the mainland should see below normal temperatures while above normal readings prevail over most other areas. Then a rapid warming trend will ultimately bring temperatures up to much above normal levels over a large portion of the state during the weekend and early next week. Rausch Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Thu-Sat, Jan 20-Jan 22. - Heavy precipitation across portions of mainland Alaska and the Aleutians, Sun, Jan 23. - High winds across portions of the Alaska Panhandle and mainland Alaska, Thu-Fri, Jan 20-Jan 21. - High winds across portions of mainland Alaska, Sat-Sun, Jan 22-Jan 23. 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