Alaska Extended Forecast Discussion National Weather Service College Park MD 735 PM EDT Wed Sep 17 2025 Valid 12Z Sun 21 Sep 2025 - 12Z Thu 25 Sep 2025 ***Periods of heavy rain and gale force winds expected from the Prince William Sound to Southeast Alaska*** ...General Overview... A rather unsettled weather pattern will remain across southern Alaska and the Panhandle region as a broad upper level low becomes anchored in place across the northern Gulf by Sunday into Monday. A second organized low pressure system crosses the Aleutians early in the week and probably reaches the northern Gulf by next Thursday with additional inclement weather. A cold front is expected to slowly sink south across the mainland and bring a steady cooling trend over the next week. ...Guidance Evaluation/Preferences... The 12Z model guidance suite initially has a good overall depiction on the overall weather pattern across the domain for the upcoming weekend, and therefore a general deterministic model blend works well as a starting point. There are some minor differences noted with the 12Z UKMET across the Gulf by Sunday, and it was also weaker with the southeast Alaska low on Monday compared to the other guidance, so less of it was used. However, the guidance overall agreed well on the consolidation of the broad upper low/trough over the Gulf by Tuesday, followed by weakening. Another difference exists across the Arctic, with the GFS maintaining a surface low/trough much longer than the non-NCEP guidance through early in the week. In regards to the next low reaching the Aleutians and Bering Sea region early next week, the GFS/GEFS are faster with the main surface low, but also has support from the AIFS guidance. The ECMWF/CMC/ECENS are slower with the low across the Bering, and these differences were mitigated with the main occluded low closer to the ECMWF, and the triple point low closer to the GFS/AIFS guidance. The trend overall has been for a faster low track compared to yesterday's forecast. The ensemble means were gradually increased to about half by next Thursday. ...Weather/Hazards Highlights... Several inches of rainfall are likely from the eastern portion of the Prince William Sound to Southeast Alaska as multiple surges of moisture move into the region, with the highest totals likely on Sunday into Monday when the onshore moisture flux is greatest. Strong winds of gale force are likely for the near shore waters owing to enhancement of the coastal barrier jet for these same general areas, especially with the low pressure system arriving on Monday into Monday night with gusts in excess of 50 mph at times. This will result in hazardous boating conditions for the coastal waters with high waves expected. The next low pressure system crossing the Aleutians and then entering the Gulf by next Wednesday and Thursday will increase rainfall prospects once again from the Alaska Peninsula to the Prince William Sound. In terms of temperatures, a gradual cooling trend is expected to commence across the mainland as a polar front slowly sinks southward through Tuesday, with subfreezing overnight lows becoming more widespread across portions of the Interior by the middle of next week. Temperatures will likely level off by mid- week across most of the mainland as the cold air advection decreases by that time. Hamrick 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