Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 704 PM EDT Sat Aug 15 2020 Valid 12Z Wed Aug 19 2020 - 12Z Sun Aug 23 2020 ...Guidance Evaluation and Preferences... The amplified pattern which has shown a strong signal in the extended guidance in recent days, appears likely to continue through the end of next week, with an upper low persisting across the Gulf of Alaska, and an upper ridge initially building across the Bering Sea by the middle of next week, spreading east across mainland Alaska late in the week. The combination of the ridge spread into the Interior, and the persistent upper low over the Gulf begins to resemble a Rex Block in ensemble guidance by next weekend, which may shift the pattern toward a less progressive state by the end of the forecast period and beyond. Model/ensemble guidance showed near to above average consensus at the large scale through the extended forecast period. A blend of the 12Z ECMWF/GFS was used heavily as a forecast starting point initially on days 4-5 (Wed-Thu). A gradual trend toward increased weight placed on ensemble means (ECENS/GEFS) was shown through time after Thu, with majority ensembles in the blend during days 7-8 (Sat-Sun). Relatively good consensus among the ensemble means by later in the forecast period helped to smooth out any differences on the details of specific features among the deterministic guidance. ...Weather Highlights/Threats... A low pressure system is forecast to cross the southern Gulf of Alaska through the middle/end of next week. This system will keep widespread precipitation in the picture across the Panhandle. Scattered rain/mountain snow showers are possible across southern mainland Alaska on Wed as a weakening frontal boundary and upper-level shortwave traverse the region. By later next week, as upper ridging builds across the Bering Sea and western mainland Alaska, drier conditions should prevail across much of mainland, with only the Panhandle/Southeast Alaska remaining wet, on the eastern side of the persistent Gulf low. Additionally, late next week, another frontal system is expected to cross the Bering Sea, and approach western mainland Alaska, spreading at least scattered showers inland with it. In general, this pattern should favor temperatures several degrees above average across much of the state. The North Slope will see somewhat cooler temperatures north of the weakening frontal boundary through the middle of next week, with high temperatures expected to be a few degrees below average. Widespread clouds and precipitation across the Panhandle will keep temperatures there several degrees through the extended forecast period. Ryan Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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