Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 622 PM EDT Fri Sep 17 2021 Valid 12Z Tue Sep 21 2021 - 12Z Sat Sep 25 2021 ...Several Major Storms to Threaten Alaska... ...Guidance and Predictability Assessment... The extended period will be an active, stormy period for Alaska and the surrounding waters as a couple of robust low pressure systems move through the Gulf of Alaska. The global guidance and their respective ensemble means are showing deeper surface lows within the mean trough over the state. Although this pattern has a higher than average predictability it continues to have spread within the timing, location and strength. While modest model input offers some detail into days 5-8, opted to maintain continuity by using mainly the compatible GEFS/ECMWF ensemble means a period of increased forecast spread with the details of stream interactions and embedded system specifics. ...Sensible Weather... A powerhouse storm is expected to track across the Gulf of Alaska early next week which will impact Kodiak Island and the south-central portion of the coast to the Panhandle with very strong maritime winds, wave threats and heavy precipitation. There will be another major and large storm that will affect the Aleutians and southern Bering Sea early-mid next week before working across the Alaskan Peninsula to the Gulf of Alaska. This storm will pack an extra punch since it will consist of additional upper-level trough energies and energies from the current West Pacific Tropical Storm Chanthu. Another round of heightened threat for high winds, waves and wrapping heavy rains. There is a threat that this system may bring a long fetch moisture plume northeastward into Southeast Alaska by later next week. Farther north in an also active stream flow around/underneath a deep closed low working over the Arctic Ocean, expect quite unsettled conditions with increased rain and snow chances, especially for the Brooks Range, with expected intrusion of Arctic air southward across the North Slope and Interior/Mainland next week. Confidence in this feature has increased with the last couple runs of the guidance and would also result in below normal temperatures for much of the mainland. Campbell Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Sep 20-Sep 21and Thu-Fri, Sep 23-Sep 24. - Heavy rain across portions of the Alaska Panhandle, Mon-Tue, Sep 20-Sep 21and Thu-Fri, Sep 23-Sep 24. - Much below normal temperatures across portions of mainland Alaska, Mon-Fri, Sep 20-Sep 24. 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