Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 643 PM EDT Sun Aug 01 2021 Valid 12Z Thu Aug 05 2021 - 12Z Mon Aug 09 2021 ...Overview and Guidance/Predictability Evaluation... An amplified and blocky ridge in place over mainland Alaska should break down early in the period as a pattern shift gets underway during the extended range. As a stagnant upper level low in the southeast Gulf of Alaska finally shifts east into Vancouver, Canada, and the ridge weakens, this should allow for troughing associated with a deep upper level low across the Bering Sea to drive a cold front into western Alaska. The Bering Sea low will meander in the region through the entire period while a couple of shortwaves/surface lows rotate around the base of the trough into the Aleutians. The guidance shows above average agreement on the overall large scale pattern through the period, with differences mostly related to the details of perturbations within the Bering Sea trough. The WPC forecast relied heavily on a blend of the 12z GFS and ECMWF through day 6, which were closer with their solutions/placement of systems to the ensemble means. To help mitigate the less uncertain details late period, the forecast leaned on the ensemble means, although modest amounts of the deterministic models were still included out through day 8 to help maintain some definition to the individual systems which tend to get washed out by the means. ...Weather/Threats Highlights... Moderate to heavy rain across the Panhandle should lessen after day 4/Thursday as the low shifts into Canada and weak ridging moves into the region. Widespread showers are also expected across western Alaska late this week as moisture surges northward ahead of the Bering Sea upper low. By Friday and into the weekend, the moisture should begin overspreading the southern and central portions of Alaska as a cold front shifts inland. Periods of showers will continue to affect the Aleutians through next weekend associated with a couple of weaker embedded surface lows. Temperatures across the state should be rather warm and 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 by Friday, temperatures should quickly trend cooler into the weekend and early next week. 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