Alaska Extended Forecast Discussion National Weather Service College Park MD 733 PM EDT Mon May 12 2025 Valid 12Z Fri 16 May 2025 - 12Z Tue 20 May 2025 ...Overview... An elongated upper low will be present over the Aleutians to Alaska Peninsula as the extended period begins Friday, and an upper low should maintain itself into next weekend and early next week as additional energy consolidates the low and moves it east through the northern Pacific/Gulf. Rounds of surface lows are possible underneath this upper low, with the strongest one likely moving through the northern Pacific south of the Alaska Peninsula over the weekend and into the Gulf early next week. This could lead to moderate precipitation and winds across the Alaska Peninsula to Kodiak Island and the Kenai Peninsula this weekend. Otherwise, rounds of light to moderate precipitation are possible generally from the Interior southward. ...Guidance Evaluation and Preferences... Model guidance at the start of the extended period is agreeable with the larger scale features of the pattern, including the Aleutians upper low and a weakening upper high over the North Slope. Smaller scale features such as the shortwaves and surface lows underneath and south of the upper low are more questionable with the details. Surface low interactions with across the southern Bering, Bristol Bay, and the Gulf make it more complex, but at least the pattern for low pressure in those areas is generally set. One notable surface low pivots through the northern Pacific south of the Aleutians Saturday and the Alaska Peninsula Sunday, moving into the Gulf early next workweek. Models show fair agreement in this low's existence but vary in the track and depth of this low. Generally models are deeper with the low's central pressure than guidance from a day ago, but show varying times of maximum depth (12Z CMC deeper and peaking earlier Saturday than the 12Z ECMWF does into Sunday). The 12Z GFS was farther east over the weekend compared to non-NCEP guidance, but ensemble means would suggest somewhere in between for its track. The details will have to continue to be refined with time. Upstream, model guidance shows quite a bit of variability with the pattern in the Bering Sea/Aleutians behind the mean trough/low, especially by early next week. While upper ridging is expected Friday-Saturday, models indicate that upper lows may emerge from the Kamchatka vicinity to flatten the ridge at times. Models have varied quite a bit with the timing and depth of the energies that may suppress the ridge and then potentially feed into the first upper/trough low. The main outlier today seemed to be the 06Z GFS that was out of phase, but additional model variability led the forecast to prefer ensemble means by the later period. The WPC forecast used a multi-model mostly deterministic blend early in the forecast period with the reasonable synoptic scale agreement. As spread increased, used more ensemble means, with the means reaching over half by Days 7-8 to mitigate the individual model differences. ...Weather/Hazards Highlights... An occluded low pressure system near the Gulf Friday will produce some moderate precipitation across Southeast Alaska and lingering light precipitation across the southern third of the Mainland or so. By Saturday precipitation should be generally light, but into Sunday an approaching surface low pressure system should spread precipitation into the Alaska Peninsula, Kodiak Island, and the Kenai Peninsula. There may be locally enhanced amounts of precipitation in favored coastal/terrain areas, but is not likely to reach hazardous levels. Will continue to monitor the strength of this surface low for any potential wind concerns, but right now winds near the southern coast look to be around the 30 knot range. Moderate precipitation looks to reach Southeast Alaska once again by early next week. With the upper low pivoting, moist inflow may reach the Interior for increasing coverage of precipitation into the weekend and early next week. Most precipitation amounts should be pretty light for the Interior, but some modest amounts could occur in the Copper River Basin. Warmer than average temperatures across the western Interior on Friday are forecast to expand eastward across the Interior this weekend and early next week, with highs in the 50s and 60s. Meanwhile, cool flow could lead to periods of cooler than normal temperatures across the North Slope into the Brooks Range. The southern third or so of Alaska should generally be warmer than average for lows but near to below average for highs in the moist and cloudy pattern there. Tate 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