Alaska Extended Forecast Discussion National Weather Service College Park MD 728 PM EDT Tue Sep 30 2025 Valid 12Z Sat 04 Oct 2025 - 12Z Wed 08 Oct 2025 ...Synoptic Overview... In the upper levels, an anchor low/trough will be in place generally across the Chukchi Sea throughout the period. A series of upper waves will rotate eastward to the south of this anchor low, which will support the development of surface lows that will keep the weather unsettled over the Bering and much of western Alaska. One such low will cross the Aleutians Friday, then move northeast over the middle of the Bering, where it will peak in intensity and bring the chance of some gusty winds and coastal flooding. Upper energy continuing eastward will bring unsettled weather along the southern coast as a fetch of moisture from the Pacific flows northward ahead of the system, with the potential for heavy rainfall along upslope portions of the coastal ranges. A leading upper-ridge will bring a period of well above average temperatures to most of the state this weekend before colder air flowing in behind brings temperatures back down to more seasonable or possibly a bit below average levels into early- mid next week. ...Guidance Evaluation and Preferences... Both the latest deterministic and ensemble guidance remain generally well clustered with respect to an upper-wave/Aleutians to Bering Sea low early in the period this weekend. The 12Z ECMWF/CMC are a bit faster and stronger with the northward progression of the surface low so the updated model blend favored a larger portion of this guidance compared to the GFS. Guidance begins to quickly diverge however early next week as the upper wave and associated surface system progress eastward across the Gulf of Alaska. The ECMWF is much faster and less amplified than the GFS/CMC as well as their respective means. The GFS and especially CMC also show the potential for reinforcing energy to help deepen low pressure over the Gulf while strong high pressure builds in more quickly behind the faster moving upper-wave in the ECMWF. This will have implications for precipitation potential into early next week along the southern coast, with the GFS/CMC and ensemble means maintaining longer-duration heavy precipitation compared to the ECMWF as troughing remains favored. While the ECens mean is slower than the ECMWF, it is also still a bit of an outlier compared to the other guidance. Another upper wave and surface low pressure system looks to approach the Bering Sea early to mid-next week, with the guidance in some disagreement about timing and location but generally well clustered to constitute a mean compromise position. The latter part of the updated blend thus begins to include a greater portion of the ensemble means while phasing out the ECMWF to account for the growing discrepancy with respect to the system evolution over the Gulf. The GEFS mean is favored which offers a compromise between the faster ECens mean and the more aggressive CMC/CMC ensemble mean. This also helped to maintain continuity from the previous forecast which favored maintaining troughing over the Gulf for a longer period. ...Weather/Hazards Highlights... As the Bering low rapidly deepens Friday as it crosses the Aleutians, winds may gust at times to near gale force, especially on the east side of the low over the central Aleutians. Gusty winds will also spread northward along the western coast as the low moves northward into the Bering Sea and closer to the mainland. Some amount of dynamic fetch may also allow seas to grow to high surf levels and bring a coastal flooding concern to Bristol Bay, where it appears the greatest likelihood for prolonged onshore flow will be. Moderate showers will also be possible across the Aleutians and along the western coast, with some precipitation reaching inland areas of the western and central Interior north to the Brooks Range as well. As the upper- wave/surface frontal system progress eastward over the Gulf later this weekend and into early next week, heavy rain will be possible at the lower elevations at times with upslope flow into the coastal ranges. This will especially be the case around Prince William Sound and east to Yakutat where several inches of rainfall can be expected. Higher elevation snow will also impact the mountains but freezing levels will remain high enough that the passes will not be affected. A strong leading upper ridge will bring a period of well above average temperatures to nearly all of the state this weekend and into early next week, with 30s for the North Slope; 40s along the western Coast and for northern portions of the Interior; and 50s for the Aleutians, Southcentral, and into Southeast Alaska. More seasonable to below average temperatures will spread eastward across the mainland early to mid-next week, with highs generally falling 10 or so degrees. The Aleutians and Southeast Alaska will remain above average. && Putnam 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