Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 626 PM EDT Tue Jul 21 2020 Valid 12Z Sat Jul 25 2020 - 12Z Wed Jul 29 2020 ...Heavy rain possible for Southeastern Alaska Sunday... ...Overview and Guidance Evaluation... Breakdown/pattern shift across the western/central Pacific has left the guidance a bit lost in how things evolve this weekend into next week. With the weakening/shift westward of the upper high over northeastern Russia, lower heights to its east (near the North Slope into Beaufort Sea) will move westward and/or northwestward, potentially in two pieces. To the south, a system out of the central Pacific may move east-northeastward and slip into the southwest side of an upper low over the Gulf, or fall just short and meander to the north. The combination of two or more scenarios in the northern/mid-latitudes has made for some disparate solutions in the recent guidance. In light of the uncertainty, favored the 12Z GFS/ECMWF to start with better agreement near the Aleutians on a slower system that may at least hold back its sfc low if not frontal structure. Kept the front progressive enough to move toward the Gulf before dissipating by Tue. This would then not favor the 12Z ECMWF that builds in ridging across much of the interior next week though keeping some percentage in the blend tempered the GFS (which kept the stronger trough moving eastward). Trended toward an ensemble mean blend with some lowering GFS/ECMWF weight to balance the larger discrepancy to the north. There, The ensembles showed strong agreement on lowering heights into NW Alaska but the deterministic models split the upper low into two pieces and move the northern component to the northwest. Such a divide between the deterministic models and ensemble means at only a day 5 lead time is pretty rare but not unexpected for a rather strong pattern. ...Weather Highlights/Threats... The best potential for highest five-day precipitation totals should be over the southeastern mainland and Panhandle. This should come with the reinforcing system over the Gulf of Sunday (leading wave on Saturday) though it will remain progressive into Canada late Sun. Lighter showers will follow in its wake as the old parent low dissipates in the Gulf. Temperatures will generally be below normal over much of the state owing to the upper trough/low. By the end of the period, temperatures should moderate somewhat but the pattern remains quite uncertain. Fracasso 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 Hazards: - Heavy rain across much of the Alaska Panhandle into southern Alaska, Sun-Mon, Jul 26-Jul 27. 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