Alaska Extended Forecast Discussion National Weather Service College Park MD 640 PM EDT Wed Sep 10 2025 Valid 12Z Sun 14 Sep 2025 - 12Z Thu 18 Sep 2025 ...Heavy rain threats into parts of coastal Southcentral Alaska next week... ...Overview... An upper trough will split in two over mainland Alaska this weekend. The northern low will retreat north into Beaufort Sea, while the southern portion dives down into the Gulf of Alaska and becomes fairly stationary over the Gulf region through early next week. Shortwave energy propagating through the Bering will amplify and impact parts of the Aleutians and Alaska Peninsula next week. ...Guidance Evaluation/Preferences... The latest guidance is more dispersed than yesterday, but still identifying general troughing from Chukchi down to Bristol Bay and the Gulf throughout the medium range period. The 12z Euro trended toward the 12z GFS and ensemble means on day 4. The Euro suite appears to capture the splitting upper trough pattern on days 5 better than the other pieces of guidance without as much spread. The GFS/GEFS maintain a separated trough pattern on day 6 while other models attempt to re-phase the two systems over the mainland. A non UK/CMC blend was utilized through most of the period with the unusual inclusion of ensemble means as early as day 4 due to higher than normal model spread. ...Weather/Hazards Highlights... A pair of surface low pressure systems are likely to bring wind and heavy rainfall to portions of the Alaska Peninsula, Southcentral mainland and Southeast Coast next week. Heavy rainfall is anticipated to return on Monday as a deepening low pressure system moves closer to the Gulf Coast. Heavy rainfall is likely to peak on Monday, which is when the frontal system should arrive along the Gulf Coast. Rainfall should continue along the coast until another low brings more rainfall to the coast on Thursday. Temperatures will likely be average to above average across the central-eastern mainland due to the trough axis extending along the west coast. Conversely temperatures will likely be below average over the West coast beneath the upper trough. Kebede Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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