Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 602 PM EDT Wed Sep 30 2020 Valid 12Z Sun Oct 04 2020 - 12Z Thu Oct 08 2020 ...Heavy rain possible Sunday for portions of coastal Southcentral to the Coast Ranges... ...Overview and Guidance/Predictability Assessment... Upper troughing is forecast to move out of southwestern Alaska/Bristol Bay late this weekend to the Gulf by the middle of next week. Upstream troughing will move into the Bering Sea around midweek next week as the flow flattens across the Pacific south of Alaska. Several embedded disturbances will rotate through/around the upper low, deforming it as additional shortwaves drop in from the northwest. The 12Z guidance offered a reasonable starting point for the forecast with better agreement overall into next week. Sunday system will likely pass just south of Kodiak toward/into Prince William Sound by early Monday (parent low). Front will lift into NW Canada with the trailing portion soutwest of Hadai Gwaii. This may allow a wave of low pressure to move northeastward along the boundary, perhaps nearing the southern Panhandle. Next system from the northwestern Pacific will enter the far western Bering around next Tue. By then, the upper pattern will start to flatten, allowing zonal flow to increase. ECMWF ensembles were still a bit quicker than the other guidance/ensembles, but the trend has been for a slightly quicker system. Nudged the forecast quicker but overall maintained good continuity. Increased ensemble weighting by next Wed/Thu as the system slips eastward, perhaps over the AKPEN. ...Weather/Threats Highlights... Low pressure will spread modest to locally heavy rainfall over southeastern-facing areas of Kodiak and the Kenai Peninsula toward Prince William Sound eastward to Yakutat Sunday, gradually diminishing as showers on Monday. Several inches of rain are possible along with breezy conditions. Less rainfall is forecast over the mainland after Monday, but will increase over the western and then central Aleutians next Tue/Wed with the next system. Progressive flow should limit heavier rainfall. Temperatures are forecast to be near to well above normal over most of the mainland, especially north of the Alaska Range. Near to below normal temperatures are forecast for the Aleutians, across portions of Southcentral, and over the Panhandle. 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 precipitation across portions of the Alaska Panhandle and southern coast of Alaska, Sat-Mon, Oct 3-Oct 5. 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