Alaska Extended Forecast Discussion National Weather Service College Park MD 622 PM EDT Thu Sep 18 2025 Valid 12Z Mon 22 Sep 2025 - 12Z Fri 26 Sep 2025 ...Heavy rain and high winds expected from Prince William Sound to Southeast Alaska early next week... ...High winds expected across the Aleutians Monday through Wednesday next week... ...General Overview... A series of upper level troughs tracking across the region will bring a couple low pressure systems with unsettled weather across the Aleutians, southern Mainland, and Southeast Alaska next week. Heavy rain and high winds are expected over Southeast Alaska early in the week as the first low pressure system stalls in the northern Gulf of Alaska. The second low pressure system will move into the Bering Sea mid-next week and gradually push across the Alaskan Peninsula into the northern Gulf during the second half of the week. This system is expected to bring high winds to the Aleutians and could bring locally heavy rain to SouthCentral and Southeast Alaska. Temperatures will generally follow a cooling trend as colder air moves in behind a polar front early next week. ...Guidance Evaluation/Preferences... At the beginning of the period, model agreement is high among the GFS/ECMWF/CMC/UKMET with all depicting the leading low pressure system stalling in the northern Gulf and ridging across the Aleutians and Bering Sea. Agreement decreases mid-next week as the second low pressure system enters the picture. The structure of this system is less consolidated and more complicated than the first system, which leads to differences in model solutions as they try to depict interactions among the different energy/wave features in the upper levels. The ECMWF and CMC are generally on the same page with a slower evolution, keeping the main upper low over the Bering through Wednesday before it shifts over the northern Gulf on Thursday. The GFS, however, is much faster with the progression, bringing the upper low into the Gulf earlier on Wednesday. Though the ECMWF-AIFS guidance is faster like the GFS, the location of the upper low is well displaced to the south compared to all other guidance, leading me to believe it is not capturing the pattern well. For WPCs afternoon forecast, a near even blend of the deterministic solutions from the GFS/ECMWF/CMC/UKMET were used for Monday and Tuesday. For Wednesday and Thursday, ensemble means from the GEFS/ECENS/CMCE were added to the blend in increasing amounts while the contributions from the deterministic models were decreased. At this point, the main influence on the deterministic portion of the blend was coming from the ECMWF while the GFS had the least influence due to noted differences above. For Friday, the deterministic solutions were removed from the blend, and the forecast was made using a near even blend of the GEFS/ECENS/CMCE. Since the means wash out details, manual adjustments were made to retain depth and definition of individual systems. ...Weather/Hazards Highlights... The low pressure system stalling in the Gulf early next week is expected to direct a plume of moisture at Southeast Alaska, and heavy rainfall is expected from Prince William Sound to Southeast Alaska, where several inches of rainfall are expected Sunday through Tuesday. In addition to heavy rain, high winds are expected along the Southeast Coast as southeasterly winds ahead of the system are enhanced by the barrier jet along the shoreline. Strong, gusty winds over the near shore waters will create hazardous boating conditions Monday into Monday night. The next low pressure system will also bring potential for hazardous weather along southern Alaska next week. High winds are expected along the Aleutians Monday through Wednesday as the system strengthens in the Bering Sea. Then, depending on the timing and strength, the system could bring another threat of localized heavy rain to SouthCentral and Southeast Alaska on Thursday or Friday. 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. Dolan/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