Alaska Extended Forecast Discussion National Weather Service College Park MD 741 PM EDT Tue May 13 2025 Valid 12Z Sat 17 May 2025 - 12Z Wed 21 May 2025 ...Overview... Much of mainland Alaska remains situated between a cyclonic gyre over the Arctic and another gyre forecast to gradually migrate from south of the Aleutians toward the Gulf of Alaska through the medium-range period. Only scattered precipitation is expected for the southern portion of mainland Alaska and the Aleutians. ...Guidance Evaluation and Preferences... Model guidance shows decent agreement on the above-mentioned pattern across the Alaskan domain through the medium-range period. A couple of modestly strong cyclones are forecast to take an east- northeasterly track to the south of the Aleutians toward the Gulf of Alaska. The first cyclone is expected to pass south of the Peninsula on Sunday, moving into the Gulf by Monday. The ensemble mean position for the cyclone appears to offer a good middle ground to mitigate the uncertainty indicated by the spread of the deterministic solutions. In the mean time, ensemble means agree well that there will be a weaker cyclone to swing around the back side of the first cyclone Sunday into Monday, followed by a tendency for the two cyclones to merge in the Gulf of Alaska toward midweek next week. There is the possibility for a third modestly strong cyclone to approach the western Aleutians by midweek but uncertainty is relatively high at his point. Meanwhile across the Arctic region, ensemble means show indications for the cyclonic gyre in the vicinity to dig a trough toward northern Alaska by early next week. The WPC forecast was based on 40% from the 12Z ECMWF/00Z EC mean, 40% from the 06Z and 12Z GFS/GEFS, and 20% from the 12Z CMC/CMC mean, with increasing proportion from the ensemble means toward the end of the forecast period. WPC continuity is well maintained. ...Weather/Hazards Highlights... The forecast period begins with a gradual trend of the general precipitation along the southern coastline of Alaska into the Panhandle to lessen with time as the associated occluded system gradually dissipates this weekend. The next cyclone should bring increasing rain chances for the eastern Aleutians on Sunday followed by the southern coastline and the Panhandle on Monday. The rain chances should then linger into midweek next week. A round of rain is expected to accompany the second cyclone across western to central Aleutians Sunday into Monday. This will be followed by a general increase of rain chances ahead of the next system which may approach from the northern Pacific by midweek. Temperatures across the central to southern section of mainland Alaska as well as the coastal plain of the North Slope should average above normal through midweek next week while the Southeast, Brooks Range, and the Aleutians should average below normal due to clouds and precipitation. Some terrain and diurnally-forced precipitation can be expected across the southern interior section near a stationary boundary while some upslope snow can be expected on the Brooks Range through the forecast period. Kong 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