Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 750 PM EDT Tue Sep 13 2022 Valid 12Z Sat Sep 17 2022 - 12Z Wed Sep 21 2022 ***Typhoon Merbok is forecast to transition to an intense extratropical low with strong winds, high seas, and coastal flooding from the eastern Aleutians to the western mainland Friday and Saturday*** ...Guidance/Predictability Assessment... The 12Z model guidance suite has above average synoptic scale agreement across the Alaska domain for the weekend, however the CMC begins diverging from the consensus by Sunday by taking the remnant low from Merbok much farther east and loses ensemble support. The ICON/JMA are also in good agreement with the GFS/ECMWF solutions for this time period. Going into early next week, the models still agree quite well on a strong ridge axis centered over the eastern Gulf, but meaningful differences emerge with the next low/shortwave approaching the eastern Aleutians and Alaska Peninsula, with the ECMWF portraying a stronger storm and the GFS weaker with two separate lows. By next Wednesday, the guidance has the general idea of another strong low entering the western Bering, although there are significant latitudinal placement differences. Taking these factors into account, the WPC fronts and pressures forecast is primarily derived from a ECMWF/GFS/UKMET blend through early Monday, and removing the CMC after Saturday night. A gradual increase in the GEFS and ECENS are incorporated for the Monday night through Wednesday time period. ...Pattern Overview and Weather/Hazards Highlights... The extratropical low from what is currently Typhoon Merbok is expected to be quite impactful as it crosses the Aleutians and then enters the Bering late this week and into the weekend. Widespread gale to storm force winds are likely across the open waters and for coastal areas, and substantial tidal flooding is probable on Saturday with strong southwesterly onshore flow. Deep southerly flow across central and western Alaska is expected to result in moderate to heavy inland rain across much of the Interior and the Brooks Range, and heavy snow for the higher elevations. This low is then forecast to weaken quickly as it lifts northward towards the Arctic Coast by Sunday and into Monday with some lingering light precipitation and diminishing winds. Farther south, a surface low is likely to develop along a front just south of the Aleutians early next week that is expected to track northeast towards the northern Gulf region. A big increase in moisture with a potential atmospheric river event directed between the Kenai Peninsula and the St. Elias Mountains, with several inches of rainfall possible Monday afternoon through Tuesday night, before the axis of heavier moisture shifts east towards the Southeast Panhandle region. By the middle of next week, another organized storm system may affect the Bering and Aleutians, although there is still quite a bit of uncertainty on specifics. Temperatures are expected to generally be in the 40s and 50s for highs on most days across most of the state, with readings generally cooling down going into next week in the wake of the Bering Sea storm. Hamrick/Wegman Hazards: - Heavy precipitation across portions of the Alaska Panhandle and southern mainland Alaska, Tue, Sep 20. - Heavy precipitation across portions of western mainland Alaska, Fri-Sun, Sep 16-Sep 18. - High winds across portions of western mainland Alaska and the Aleutians, Fri-Sat, Sep 16-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