Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 601 PM EST Fri Jan 17 2020 Valid 12Z Tue Jan 21 2020 - 12Z Sat Jan 25 2020 The large scale pattern across Alaska during the extended forecast period is forecast to be strikingly different than that seen during the short range. A mean trough/upper low is forecast to develop/persist across the Arctic Ocean north of Alaska and Siberia through the extended forecast period, with an active storm track across the North Pacific, generally south of the Aleutians, and into the Gulf of Alaska, and upper ridging shifting eastward into west central Canada. Models/ensemble today have shown a trend toward developing a negatively tilted upper ridge axis from the Gulf of Alaska across the Alaska Peninsula and into the eastern Bering Sea by late next week. If this occurs, it would allow for the potential for shortwave energy originating in the arctic to amplify and dive southeastward around the eastern side of the ridge, potentially affecting eastern portions of Alaska. A series of low pressure systems are forecast to track eastward south of the Aleutians and toward the Gulf of Alaska through the forecast period, as part of the active North Pacific storm track mentioned above. Model spread with respect to these systems increases gradually through time, with ensemble means offering a more consistent picture especially toward the middle and end of the forecast period. In general, this setup should keep precipitation chances elevated across much of the Alaska Panhandle/Southeast Alaska into much of next week, with heavy precipitation possible early next week. Drier conditions should prevail across much of the remainder of mainland Alaska. As the negatively tilted upper ridge axis amplifies across the Alaska Peninsula late next week, most deterministic solutions show the potential for arctic shortwave energy to dig southward into eastern portions of the Interior and perhaps even as far south as the Panhandle. Solutions vary on the precise timing and structure of such a feature, but this would result in the potential for colder air to once again move into the North Slope and eastern portions of the Interior. In contrast to yesterday, where the GFS appeared to be quite well-centered within the ensemble spread, no one piece of deterministic guidance today stood out as being more well-centered than others within the ensemble spread. Thus, a multi-model deterministic blend, including the 12Z ECMWF/GFS/CMC was used as a forecast starting point early in the extended period. Weight place on ensemble means was increased through time, with a majority of the blend based on ensemble means starting on day 6 (Thu) and onward. Ryan Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php - Heavy precipitation across portions of the Alaska Panhandle, Mon-Tue, Jan 20-Jan 21. - Much below normal temperatures across portions of mainland Alaska, Mon, Jan 20. 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