Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 653 PM EDT Sat Aug 22 2020 Valid 12Z Wed Aug 26 2020 - 12Z Sun Aug 30 2020 ...Overview and Guidance Evaluation/Preferences... Recent adjustments in the guidance have led to significantly better clustering for the strong system expected to track into the Aleutians and Bering Sea by late week/weekend. Overall trends in the past couple days have been slower and southward, with earlier solutions that were on the eastern side of the spread (including the 00Z ECMWF and pre-00Z GFS runs) adjusting westward. Also the consensus has gathered toward recent days of ECMWF/ECMWF mean solutions that have generally advertised fairly early and strong development. Helping to improve confidence is that the 12Z GEFS mean finally shows a strong evolution after a number of runs were inconsistent and generally quite weak. Even with the improved agreement, there may be multiple sources that contribute to the upper dynamics so the potential remains for some further adjustment. Farther east the models and ensemble means have settled into good agreement for the upper low tracking from the southeastern Bering Sea/Bristol Bay through the Gulf of Alaska Wed onward. There are still some small-scale differences for the surface system which have low predictability several days out in time. After this system departs expect an upper ridge to build into the Northeast Pacific and southeastern mainland/extreme western Canada. Meanwhile the northern mainland and vicinity will be under or a little south of a col region between features to the south/southwest and upper ridging north of Russia/an upper low near the Canadian Archipelago. There is somewhat more of a signal today that flow aloft could push a cold front into the northeast corner of the mainland. In light of the better than average guidance guidance agreement that extends even to the end of the period, today's forecast was able to hold onto 75 percent total weight of the 12Z ECMWF/GFS/CMC out to day 8 Sun after starting with all operational model input early in the period. The minority ensemble weight came from the 12Z GEFS/00Z ECMWF means. ...Weather Highlights/Threats... The much-improved agreement in latest guidance provides increasing confidence in a strong storm system bringing a broad area of precipitation and strengthening winds across the Aleutians and Bering Sea after midweek. The enhanced winds and precipitation with the leading fronts should reach the Alaska Peninsula and the southwestern third to half of the mainland after Fri. The system tracking from Bristol Bay and southwest corner of the mainland through the Gulf of Alaska mid-late week will bring some focused precipitation to areas along the southern coast and Panhandle, with broader coverage of less intense/organized activity elsewhere. Expect a drier trend from west to east before the approach of moisture ahead of the Aleutians/Bering Sea storm. The southern-southeastern mainland/Panhandle as well as a majority of the North Slope will see below normal highs most of the period, with the former tending to see the coolest anomalies. Near to above normal highs are likely over some central mainland areas and over the west. There will be greater coverage of above normal readings for low temperatures. Highest anomalies for lows should be over the northern mainland mid-late week and then shift to the southwestern mainland next weekend with the arrival of wind/moisture. Rausch 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