Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 549 PM EST Fri Dec 13 2019 Valid 12Z Tue Dec 17 2019 - 12Z Sat Dec 21 2019 Models were relatively agreeable during the first portion of the extended forecast period, and a blend of the ECMWF/GFS was used as a forecast starting point during days 4-5 (Tue-Wed). These solutions showed relatively small timing and structural differences with a low pressure system passing near the eastern Aleutians and the Alaska Peninsula during that time, and the described blend should resolve these differences favorably. From day 6 (Thu) onward, this system is forecast to move eastward into the Gulf of Alaska. Timing differences among the guidance increase from Thu onward, and a weighting of ECENS/GEFS ensemble means in the forecast was increased to account for this increased spread. Models/ensembles show some broad agreement that another relatively deep low pressure system should enter the western Bering Sea by day 6 (Thu), with guidance showing continuing to show some relatively large timing/structural differences that are best resolved at this point in time by going heavily toward the ensemble means. Farther north, persistent upper level ridging across the Arctic Ocean is forecast by ensembles to gradually shift toward Siberia, allowing lower heights (potentially an upper low) to spread into the North Slope and the Alaska interior by the middle of next week. Models/ensemble agree on this general scenario but show variability on the specific timing of individual upper waves as well as the possible consolidation of energy into an upper low. Further warranting increased use of ensemble means through time. Some continued use (20-40%) of deterministic solutions was warranted through the end of the forecast period, however, to add a bit of definition to features beyond that shown by the ensemble means. This pattern should initially favor wet conditions across southern mainland Alaska early in the extended period, the axis of best moisture should shift east into the Panhandle/Southeast Alaska from the middle of next week onward. Farther north, initially above average temperatures across much of the Interior will be replaced by below average temperatures as upper heights fall by early next week. Dry conditions should prevail across most of the Interior, however. Ryan Additional 3-7 Day Hazard information can be found on the WPC medium range hazards https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: -Heavy precipitation across portions of the Alaska Panhandle, Mon-Tue, Dec 16-Dec 17. 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