Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 526 PM EDT Mon Sep 12 2022 Valid 12Z Fri Sep 16 2022 - 12Z Tue Sep 20 2022 ...T.S. Merbok to intensify to Typhoon then transition to a vigorous extratropical low with threat for heavy winds/seas/precipitation from the Aleutians/Bering Sea to the western/northern mainland Thursday-weekend... ...Guidance/Predictability Assessment... The 12 UTC GFS/ECMWF now seem to have a much handle on the upper pattern evolution through medium range time scales and importantly for dangerous Merbok that the similar GFS/ECMWF track as a powerful extratropical low from the Aleutians/Bering Sea through western/northern Alaska most in line from with the latest JTWC advisory, bolstering forecast confidence. This obviously presents a significant Thursday through weekend maritime to inland high winds/waves and heavy rainfall (Interior/Brooks Range snow) hazard that is highlighted in the WPC PMDAK discussion headline and the collaborated WPC Hazards Outlook. The GFS/ECMWF are also generally compatible with most other features through medium range time scales, albeit with some timing/focus differences that seem to be mitigated consistent with predictability by the aforementioned blend process. Opted to not blend in generally supportive ensemble guidance to allow as much system integrity and detail as feasible in this stormy pattern. ...Pattern Overview and Weather/Hazards Highlights... The deep extratropical low associated with Merbok will spread a threat for heavy winds/seas and the influx of tropical moisture should support heavy downpours/rainfall from the Aleutians/Bering Sea Thursday/Friday to the western/northern mainland and southern Arctic Ocea Friday/weekend. There is also a concurrent weekend threat for heavy/windy mountain focusing snows up through the Brooks Range. Meanwhile, lead late week northern stream upper trough and Gulf low genesis will support lingering moderate to locally heavier rains and mountain snows from south-central to southeast Alaska with system proximity and inflow. There is a growing guidance signal to rejuvinate northern Gulf of Alaska low developments over the weekend and especially into early next week with upper trough digging with periodic intrusion of impulses sliding underneath the main high latitude low. This along with potential infusion/phasing of less certain North Pacific low energies/deepened moisture into the Gulf is expected to combine to bring emerging later period rounds of unsettled weather inland into the southern coastal section and the Southeast Panhandle. Upstream, there is also a growing guidance signal to develop and bring another well defined low/frontal system from mid-higher latitudes into the Bering Sea/Aleutians early next week that offers some potential for long fetch moisture inflow to also monitor at these less certain longer time frames. Schichtel Hazards: - Heavy precipitation across portions of mainland Alaska, Thu-Sat, Sep 15-Sep 17. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Thu-Fri, Sep 15-Sep 16. - High winds across portions of mainland Alaska and the Aleutians, Thu-Sat, Sep 15-Sep 17. 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