Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 426 PM EDT Sat Apr 21 2018 Valid 12Z Wed Apr 25 2018 - 12Z Sun Apr 29 2018 ...Guidance/Uncertainty Assessment... Models/ensembles show decent agreement with respect to a large upper low/deep surface low over the southern Bering Sea at the beginning of day 4 (12Z Wednesday). A secondary low developing farther east along the occluded front is forecast to move north across the Bering, just off the west coast of Alaska. The associated surface front is forecast to move east across the Gulf of Alaska before gradually dissipating. While the upper low is forecast by all guidance to linger across the southern Bering, and slowly drift southeastward toward the Gulf by late next week, guidance shows some degree of shortwave ridging building across the Bering between the upper low and the next system. With increasing model spread during the second half of the forecast period, ensemble mean (00Z ECENS/06Z GEFS) weighting was increased to a majority of the forecast blend during days 6-8 (Friday through Sunday). ...Weather/Threats Highlights... Enhanced onshore flow is expected for southeastern Alaska and the Aleutians for the middle of next week east of the strong Bering Sea low pressure system. Heavier precipitation is likely from Anchorage to Juneau, especially across mountainous terrain. Farther north, the upper low will also produce scattered rain/snow showers across the Yukon Valley. The lingering upper low slowly drifting southeastward will keep scattered precipitation chances across these same general locations through Friday. By late in the week, rain/snow and potentially gusty winds may begin spreading across the Aleutian Chain as the next significant storm system approaches. Temperatures will be near or several degrees above average through the period across most of the state. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html D. Hamrick