Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 510 PM EDT Thu Sep 03 2020 Valid 12Z Mon Sep 07 2020 - 12Z Fri Sep 11 2020 ...Dynamic Storm Pattern for Alaska... There is a strong guidance signal showing that amplified upper trough development out through the Bering Sea will support storm genesis. The deepened low will lift northward along or just off the west coast (eastern Bering) into the Seward Peninsula early next week and support a swath of high winds/seas and locally heavy precipitation. Models and ensembles continue to cluster near the ensemble means, and a blended/consensus solution of the compatible 12 UTC GFS/ECMWF/UKMET serves as a good forecast starting point Monday-Wednesday. Ample moisture will pump inland to the interior through the very heavy rain supported southern tier of the state in deep layered southwesterly flow channeled between the storm and an amplifying downstream upper ridge. Upstream extratropical transition of Typhoons Maysak and Haishen over northeastern Asia also supports strong ridge/trough couplet development and maintenance over eastern Asia/Bering next week. Later, there is also a less certain but emerging guidance signal favoring additional low development into the Aleutians in about a week in the wake of the lead storm, but it still too early to tell given guidance forecast spread if this may lead to another surge of deep moisture from the mid-latitudes/sub-tropics. An ECMWF ensemble mean solution, along with some manual adjustments to insure a deepened low consistent with favorable upper troughing, seems to provide max WPC continuity and offer the threat potential. Schichtel 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 precipitation across portions of mainland Alaska, Sun-Mon, Sep 6-Sep 7. - Heavy rain for parts of the Alaska Panhandle and mainland Alaska, Sun-Wed, Sep 6-Sep 9. - High winds across portions of mainland Alaska, Sun-Mon, Sep 6-Sep 7. 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