Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EDT Sun May 03 2020 Valid 12Z Thu May 07 2020 - 12Z Mon May 11 2020 ...Guidance/Predictability Assessment... Models/ensembles show relatively good consensus at the large scales through the extended forecast period, with a persistent trough/upper-level low south of Alaska across the North Pacific, and an upper-level ridge axis building from western Canada into mainland Alaska next week. This setup will eventually result in a pattern resembling a Rex Block, that will persist through the end of the extended forecast period. Even at smaller scales, deterministic model consensus is above average during days 4-5 (Thu-Fri) as one low pressure system slowly weakens south of the Gulf of Alaska and another weakens across the western Bering Sea. The above average consensus during this time frame lent to the use of a 12Z ECMWF/GFS blend during days 4-5. By days 6-8 (Sat-Mon), the preferred storm track does not change substantially, but guidance spread gradually increases through time with the next low pressure system potentially approaching the western Aleutians by Sat, although consensus on this system has improved a bit compared to yesterday. Spread is highest days 7-8 with respect how this surface low evolves over the western Bering Sea, and whether a triple point low develops farther southeast closer to the Aleutians. Given the decent large scale agreement, opted to gradually increase weighting of ECENS/GEFS ensemble means through time, with majority weight on the means by days 7-8. ...Weather/Hazard Highlights... Persistent low pressure south of the Gulf of Alaska will keep onshore flow and precipitation, along with gusty winds, in the picture for the Alaska Peninsula and portions of southern mainland Alaska through the forecast period, especially Thu-Fri as a weakening frontal boundary approaches. The western/central Aleutians will be subject to a couple rounds of rain and gusty winds Thu and again Sat-Sun as frontal systems affect the region. Rising heights across mainland Alaska as the upper ridge builds will promote warming temperatures. High temperatures are forecast to be 5 to 15 deg F above average across much of mainland Alaska from the middle of the week into the weekend, with temperatures forecast to rise into the 60s (possibly even approaching 70) for portions of the Interior. 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