Alaska Extended Forecast Discussion National Weather Service College Park MD 700 PM EDT Tue Sep 9 2025 Valid 12Z Sat 13 Sep 2025 - 12Z Wed 17 Sep 2025 ...Heavy rain threats into parts of coastal Southcentral Alaska later this week, and again by next Tuesday... ...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 portions of the Aleutians and Alaska Peninsula next week. ...Guidance Evaluation/Preferences... A GFS-ECMWF centric blend was utilized throughout the medium range period. The deterministic UKMET and Canadian were not used in today's blend because they diverged too much from each other as well as consensus. The 12z Euro trended toward the 12z GFS and away from the Canadian/UKMET in regards to the separating upper trough over the Alaska Peninsula on day 4. 12z GEFS and 00z ECE were introduced to the blend on day 5, but the deterministic GFS and EC were favored to retain smaller scale details. The Canadian ensemble was introduced on day 6, with equal weighting between individual blended elements. The ensembles were favored on days 7 and 8 due to increased variance in the deterministic guidance. ...Weather/Hazards Highlights... A deepening surface low pressure system is likely to bring wind and heavy rainfall to portions of the Alaska Peninsula, Southcentral mainland and Southeast Coast this weekend. Heavy rainfall is anticipated to begin on Friday as the 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. 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