Alaska Extended Forecast Discussion National Weather Service College Park MD 756 PM EDT Fri May 23 2025 Valid 12Z Tue 27 May 2025 - 12Z Sat 31 May 2025 ...General Overview... Much of mainland Alaska will generally be sandwiched between two upper-level gyres during much of the medium-range period. One gyre rotating over the Arctic Ocean will send disturbances toward the North Slope while the other gyre will continue to send disturbances from the Bering Sea and North Pacific eastward toward the Gulf of Alaska and the Alaska Panhandle. By late next week, there is decent model agreement for a negatively-tilted upper ridge to establish over mainland Alaska. ...Guidance Evaluation and Preferences... With the presence of numerous smaller scale disturbances embedded within the aforementioned two upper-level gyres, the predictability of individual disturbances beyond Day 5 is lower than normal. The largest model uncertainty appears to be located just north of mainland Alaska where models are showing difficulties in predicting the timing and location of a potential closed low during midweek next week. This closed low/trough is then forecast to lift back into the Arctic late next week, which coincides with decent agreement for a negatively-tilted upper ridge to establish over mainland Alaska. For the southern tier of Alaska including the Aleutians, models are in good agreement for a number of disturbances/cyclones to converge over the Gulf of Alaska next week followed by gradual dissipation of the merger late next week. There is also decent agreement shown by the ensemble means for the next cyclone to reach the western Aleutians by next weekend, although the deterministic solutions place the cyclone center much farther to the south. The WPC forecast package today is based on the consensus of the 12Z ECMWF/00Z & 12Z EC mean (40%), 12Z GFS/06Z & 12Z GEFS (40%), and 12Z CMC/CMC mean (20%) with ensemble means comprising the vast majority toward the end of the forecast period. WPC continuity is well-maintained. ...Weather/Hazards Highlights... Periods of rain and high mountain snow are expected from the Alaska/Kenai Peninsulas to the southeast Panhandle region, with the greatest coverage and intensity expected from Juneau and points south, where heavy rain appears most likely Wednesday and Thursday of next week, while heavy snow can be expected for the high-elevations. Farther inland across the interior section of mainland Alaska, scattered afternoon and evening thunderstorms are likely to develop in the presence of an unstable airmass, mainly between Anchorage and Fairbanks. There is a tendency for these activities to expand toward northeastern Alaska by late next week as southerly flow begins to establish under the above-mentioned upper-level ridge. Lightning strikes from these storms may increase the threat of wildfires in the region. Temperatures overall are expected to be near to slightly above average for late May standards across the central and southern mainland, and slightly below north of the Brooks Range. Cooler conditions are also likely for the coastal areas and the near shore islands owing to increased cloud cover and rainfall. 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