Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 317 PM EDT Sat Sep 15 2018 Valid 12Z Wed Sep 19 2018 - 12Z Sun Sep 23 2018 While models/ensemble generally show good large scale agreement across Alaska during the medium range, there are some significant points of contention that remain unresolved. Models continue to show difficulty handling a relatively small scale but amplified shortwave of Arctic origin, which is expected to be near the Bering Strait on day 4 (Wed). Solutions continue to differ as to whether the feature will dig southeastward across Alaska, reaching the Gulf by Fri, or whether it will follow a more eastward course along the Arctic coast into Canada. The GFS and ECMWF have both flipped between these two ideas, thus confidence remains low in this particular aspect of the forecast. Additionally, the North Pacific upper ridge axis initially centered across the Bering Sea and Aleutians is still expected to weaken somewhat and shift eastward during the medium range period. Models continue to show differing solutions, however, as to the extent of weakening that the ridge will undergo. Nonetheless, the eastward shift in the ridge will allow upper troughing to amplify across the Bering Sea by mid to late next week, setting up a period of moist southwesterly flow across the Aleutians and into much of mainland Alaska. A majority deterministic multi-model blend including the ECMWF/GFS/CMC was used a basis for the forecast during days 4-5, with majority weighting of the ECENS and GEFS means for days 6-8. In terms of sensible weather, this pattern should favor near to above average temperatures across most of Alaska through the extended period. As the ridge moves east and southwesterly mid/upper flow takes hold by mid to late next week, expect increasing coverage of precipitation from the Aleutians eventually spreading into mainland Alaska as upper troughing amplifies across the Bering Sea and a frontal system approaches. Ryan WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html