Alaska Extended Forecast Discussion National Weather Service College Park MD 700 PM EDT Wed May 14 2025 Valid 12Z Sun 18 May 2025 - 12Z Thu 22 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. Scattered precipitation is expected for the southern portion of mainland Alaska and the Aleutians, while the Panhandle possibly receives moderately heavy amounts from early to middle of next week. ...Guidance Evaluation and Preferences... Model guidance shows decent agreement on the above-mentioned pattern across the Alaskan domain through the medium-range period. Deterministic model solutions today show a wider west-to-east spread on the position of a modestly strong cyclone passing south of the Alaska Peninsular early on Day 4/Sunday, with the 12Z ECMWF taking it on the fastest and furthest east track compared with the 06Z and 12Z GFS which place the cyclone center on the western half of the spread; the 12Z CMC is in between the GFS and ECMWF positions. The EC ensemble mean as well as model consensus yield a cyclone position near the middle of the spread over the Gulf of Alaska Sunday morning--a position that agrees very well with WPC continuity. This system is forecast to head toward Alaska Panhandle and weaken with time through midweek next week. Models today generally indicate somewhat higher precipitation totals for the southern half of the Panhandle beginning Monday of next week, lingering through midweek while gradually becomes lighter. A couple more waves or weaker cyclones are forecast to follow through midweek. Models and ensemble means show good agreement for a wave/weak cyclone to swing around the back side of the lead cyclone near the western to central Aleutians Sunday into Monday. The wave will continue to head east across the Gulf of Alaska and merge with the remnants of the first cyclone through midweek. Models and ensembles show better agreement on a third wave/cyclone to approach the western Aleutians by midweek although uncertainty remains relatively high. The ECMWF/EC mean as well as the CMC/CMC mean are showing a better-defined triple-point low to develop midweek over the central Aleutians. These solutions are in better agreement with the GFS clusters which tend to indicate a stronger cyclone to pass just south of the Aleutians midweek. However, the 18Z GFS has shifted the cyclone track farther north to agree with the ensemble mean consensus. Meanwhile across the Arctic region, ensemble means continue to indicate a cyclonic gyre in the vicinity will dig a trough toward northern Alaska by early next week before showing signs of lifting back north by Day 8/next Thursday. 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... As the medium-range forecast period begins on Sunday, precipitation along the southern coastline of Alaska into the Panhandle should be tapering off. However, the next cyclone should quickly bring increasing rain chances from the southern coastline to especially the Panhandle on Monday. The rain chances should then linger into midweek next week with an upward trend on precipitation amounts comparing with yesterday's model runs. 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 shows a better chance of development over the central Aleutians 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