Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 548 PM EDT Wed Aug 26 2020 Valid 12Z Sun Aug 30 2020 - 12Z Thu Sep 03 2020 ...Overview...Preferences...and Weather Highlights/Threats... ...A major cyclone is forecast over the weekend into early next week 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, and then weaken as it drifts inland into northern Alaska by midweek. The latest model guidance showed above average agreement for the end of August to early September. The agreement led to a consensus-based forecast, with a blend of the 00-12Z ECMWF/12z CMC/00z ECMWF Ensemble Mean/06z GEFS Mean used in composing the fronts and adjusted sea level pressures. Overall, there is good continuity in the forecast. The 12z ECMWF trended a bit faster than its prior progs and the other 12z models. The blend mitigated the timing difference by taking a consensus approach. Expect a broad area of precipitation and stronger winds (gales likely to locally storm conditions possible) to accompany the storm forecast to track from the North Pacific across the Aleutians into the southern Bering Sea and southwest Alaska. 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 into early next week along the southern coast and over favored terrain inland from the coast, and this includes areas down stream, all the way to the panhandle of AK. The peak 850 mb moisture fluxes cross the upper Aleutians late in the weekend into southwest Alaska as the system approaches, adding support to heavy rain potential. 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