Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 544 PM EDT Tue Aug 25 2020 Valid 12Z Sat Aug 29 2020 - 12Z Wed Sep 02 2020 ...Overview...Preferences...and Weather Highlights/Threats... ...A major cyclone is forecast over the weekend to impact the Aleutians to southwest Alaska... Guidance continues to advertise a significant large-scale pattern change toward a mean upper low over the Bering Sea and downstream ridge aloft building over the Northeast Pacific and eastern mainland/western Canada. There is good agreement that a strong North Pacific storm will develop and cross the Aleutians and move into southwest Alaska. The latest model guidance showed above average agreement for the end of August to early September. This allowed for a heavy weighting of the available deterministic guidance to be used (00-12Z ECMWF/12z GFS/12z CMC) with minority weighting of the 00z ECMWF Ensemble Mean to help retain continuity in the forecast. Expect a broad area of precipitation and stronger winds to accompany the storm forecast to track from the North Pacific across the Aleutians into the southern Bering Sea and southwest Alaska. The system has potential to produce storm force winds. Showers with a lead wave and associated warm/moisture advection stream onshore into the Alaska Peninsula and then extend across into southeast Alaska/panhandle by the end of the weekend. Significant precip totals will be possible this weekend along the southern coast and over favored terrain inland from the coast. Clusters of showers are also expected in advance of the upper trough across the upper Aleutians and western Alaska into early next week before gradually decreasing on coverage by mid week as the low decays as it heads inland. Below normal highs will develop over western Alaska as the cyclone arrives. This, combined with the clouds and showers. should promote below normal temperatures early to middle portions of next week over western Alaska. Cool temperatures are forecast to persist north of a stationary front in northern Alaska. Warm advection ahead of the Aleutians/Bering Sea/southwest AK storm should spread warmer temperatures across much of southern AK during the weekend and early next week. Petersen 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 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