Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 629 PM EDT Sat Jul 31 2021 Valid 12Z Wed Aug 04 2021 - 12Z Sun Aug 08 2021 ...Overview and Guidance/Predictability Evaluation... An amplified upper level pattern should be in place to begin the extended range on Sunday with a blocky ridge across mainland Alaska keeping deep troughing in both the Gulf of Alaska and the Bering Sea. The ridge will limit the overall eastward progression of the Bering Sea low, and should force shortwave perturbations northward across the eastern Aleutians and western Alaska. The ridge over the mainland should begin to break down by day 6/Friday which would allow upper troughing to move into Alaska, while the Bering Sea low rotates slightly eastward next weekend. The guidance shows above average agreement on the overall large scale pattern through the period, with differences mostly related to a couple of shortwaves/surface lows rounding the base of the Bering Sea trough. The WPC forecast for days 4-6 was based on a majority deterministic model blend between the 12z GFS, ECMWF, and CMC. After that, the forecast trends towards the ECENS and GEFS ensemble means to help mitigate the less uncertain details. Although, at least half of the deterministic guidance was still included even at day 8 which helped maintain some definition to the individual systems which tend to get washed out by the means. ...Weather/Threats Highlights... The best chance for rain for the first half of the period should be across portions of the eastern Aleutians/Alaska Peninsula into parts of the west coast as moisture continues to surge northward ahead of the Bering Sea upper low. Moderate to locally heavy rain is also expected across parts of the Panhandle region Wednesday and Thursday as a second upper low meanders in the area before eventually shifting into Vancouver, Canada. By Friday and into the weekend, expect moisture to begin overspreading the southern half of the mainland as a cold front shifts inland, with showers also continuing across the Aleutians associated with a couple weaker embedded surface lows. Temperatures across the state should be above to well above average for most of the region underneath of the strong upper level ridge. As the ridge begins to break down and troughing moves into the state, temperatures should trend cooler into the weekend. Portions of the North Slope region could see daytime highs 10-15 degrees below normal as a shortwave drops southward from the Beaufort Sea. Santorelli 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