Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 546 PM EDT Wed Sep 02 2020 Valid 12Z Sun Sep 06 2020 - 12Z Thu Sep 10 2020 ...Heavy rain early next week over much of the coast... Robust system out of the central Pacific will bring heavy rain and windy conditions to the Alaska Peninsula eastward across Kodiak/Kenai toward the Panhandle early next week. Rainfall amounts could be 5-10 inches over the first few days of the period with higher local amounts in favored areas but lower amounts in shadowed areas. Main parent low will lift northward along or just off the west coast (eastern Bering) into the Seward Peninsula with another swath of locally modest/heavy rain. Models and ensembles continue to cluster near the ensemble means, and a blended/consensus solution of the latest 12Z guidance served as a good starting point. UKMET became notably quicker with the system by Tue as it moves NNE then NE over far NW Alaska, and was discounted. However, overall trend was a bit quicker but not to that extent. Slowly moving cold front in meridional flow will pump ample moisture into the region up and over the Alaska Range as a warm front jumps northward. Milder air will surge northward as well, but will be replaced by a bit cooler air behind the front. For next Wed/Thu, another system out of the western Bering will dip near the western Aleutians, but the models remained spread out. Trended toward the ECMWF ensemble mean which was closer to continuity than the GEFS mean and tends to perform better in amplified flow. Upstream extratropical transition of Typhoons Maysak and Haishen will likely lead to a strong ridge/trough couplet over eastern Asia/Bering around the middle of next week. Too early to tell if this may lead to another surge of moisture from the mid-latitudes/sub-tropics. 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 portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Sep 6-Sep 8. - Heavy rain across portions of mainland Alaska, Sun-Mon, Sep 6-Sep 7. - 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