Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 636 PM EDT Tue May 26 2020 Valid 12Z Sat May 30 2020 - 12Z Wed Jun 03 2020 ...Overview and Weather Hazards/Threats... A mid/upper-level ridge centered across the arctic just north of Alaska is expected to slowly weaken through the extended forecast period. The ridge will promote well above average temperatures for much of mainland Alaska (especially western mainland and the Interior) over the weekend, persisting into early next week - with forecast highs ranging from 5 to as much as 20 deg F above average. Temperatures may approach 80 deg at a few locations across the Interior. Meanwhile, an active and somewhat blocked pattern farther south will keep persistent negative height anomalies in place across the North Pacific from near/south of the Aleutians east into the Gulf of Alaska. A pattern with some degree of blocking across the northern hemisphere should favor a slower/less progressive evolution of features across the North Pacific and Alaska, and this concept guided, to some extent, the model preference today (see below). An initially deep barotropic low in the Gulf of Alaska on Sat is expected to gradually fill/weaken through the weekend as another low pressure system slowly traverses the Aleutians, with a new triple point low forecast to develop in the Gulf of Alaska by Mon or Tue. The leading system in the Gulf of Alaska will keep onshore flow in place, with scattered areas of precipitation (more widespread in favored upslope areas) in southern mainland and Southeast Alaska. Areas of showers will also cross the Aleutians over the weekend in association with the next system. As the triple point low develops in the Gulf by early next week, precipitation across southern mainland Alaska could become more widespread, with moisture (and scattered precipitation) eventually spreading north into portions of the Interior toward the middle of next week. ...Guidance/Predictability Assessment... A blend of the 12Z ECMWF/CMC was used as a basis for the forecast during days 4-5 (Sat-Sun). The GFS was excluded from the blend for this forecast cycle, as it seemed to be an outlier with moving a deep upper low east into the Gulf of Alaska much more quickly than the overall model/ensemble consensus. Additionally, the GFS weakened the arctic ridge more quickly than the other guidance, opening the Interior up to stronger easterly flow sooner than the overall consensus. Starting on day 6 (Mon) and continuing through day 8 (Wed), weighting of ensemble means (ECENS and NAEFS) was gradually increased through time, with majority weight on ensemble means by days 7-8. 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 Hazards: - Much above normal temperatures for portions of mainland Alaska, Fri-Tue, May 29-Jun 2. 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