Alaska Extended Forecast Discussion National Weather Service College Park MD 624 PM EDT Thu Sep 4 2025 Valid 12Z Mon 08 Sep 2025 - 12Z Fri 12 Sep 2025 ...A deep cyclone will bring a rain and wind threat from the Aleutians to the Southern Coast and Southeast... ...Guidance Evaluation/Preferences... The main feature of interest during the medium range period (next Monday to Friday) is a deepening cyclone which should reach the west-central Aleutians by Monday. This cyclone likely has connections to Tropical Storm Peipah which is currently near Japan. For the past couple of days, the guidance has more or less locked in on the presence of a significant storm, but both the track and timing remain highly variable. As of the 12z guidance this afternoon, the GFS and ECMWF seem most consistent with the ensemble means through much of next week showing the cyclone skirting the north side of the Aleutians into the Bering Sea moving into western Alaska around next Wednesday or Thursday, and with a possible weaker triple point low development in the Gulf which should enhance moisture and precipitation development along the Southern Coast region and parts of the Southeast. The CMC and UKMET today are a southern outlier bringing the storm well south of the Aleutians and were not included in todays blend. It is important to note though that the timing and track forecast is low confidence still as all models continue to show run to run variability (flipping from north of the Aleutians to south). It does seem likely though that the parent trough of this system may be slow to move out of Alaska later next week due to a building upper ridge downstream over northwestern Canada. The WPC blend for today blended the GFS and ECMWF with increasing amounts of the ensemble means through the period. Did weight the ECMWF slightly more than the GFS since it was closest to the ensemble means (the GFS was a little slow late period with the low in the Bering Sea). Overall, this maintained fairly good continuity with yesterdays forecast as well. ...Weather/Hazards Highlights... Following a weakening initial cyclone moving into Western Alaska this weekend, the pattern continues to trend more active next week. The initial cyclone may continue to bring rain showers across much of the Mainland Sunday into Monday with some enhancement near favorable mountain ranges. The next, deeper, cyclone will approach the Aleutians Sunday into Monday bringing both a high wind and heavy rain threat to at least central to eastern Aleutians. As this system advances eastward, moisture will move into the Peninsula and eventually western Alaska. Models are showing better consensus today on a likely heavy rainfall threat for parts of the Southern Coast and Southeast Alaska next Tuesday through Thursday, with several inches of rainfall possible over a multi-day period. There remains a lot of uncertainty still on the exact track of the system and the dynamics as it gets closer to mainland Alaska which of course will have significant implications on the heavy rainfall threat. There was enough of a model signal though to add a heavy rain area to the WPC Hazards map for today. This system will likely spread rain, though lighter, into parts of the Mainland as well next week. Temperatures across much of Alaska will trend colder next week underneath of upper level troughing. Southeast Alaska and the Panhandle region look to be near or above normal given underneath of stronger upper level ridging. Santorelli 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