Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 750 PM EDT Thu Sep 15 2022 Valid 12Z Mon Sep 19 2022 - 12Z Fri Sep 23 2022 ...Guidance/Predictability Assessment... The 12Z model guidance suite has good synoptic scale agreement across the Alaska domain for early next week, however the GFS begins diverging from the outset on Monday with the next low approaching the eastern Aleutians, with a position south/slower of the ensemble means and the CMC/ECMWF. Going into Tuesday, the models still agree quite well on a strong ridge axis centered over the eastern Gulf and western Alaska, but meaningful differences remain with the next low affecting western Alaska, with the GFS both slower and weaker than the EC/CMC ensemble. By Wednesday, the guidance has the general idea of another strong low entering the western Bering, although there are significant placement differences, with the GFS well ahead of the better clustered, but increasingly divergent CMC/ECMWF solutions by this time. Taking these factors into account, the WPC fronts and pressures forecast is primarily derived from a multi-deterministic blend through Wednesday, leaving out all deterministic GFS. A gradual increase in the GEFS and ECENS are incorporated for the latter half of the forecast period. ...Pattern Overview and Weather/Hazards Highlights... The lingering effects of the remnants of Merbok will remain over the Chukchi Sea to start the extended period on Monday. Expect continued upslope rains into the western Brooks Range and along the Arctic coast. Meanwhile a second developing low will track almost due north across the AKPEN into Bristol Bay and Southwest Alaska by Monday night. Expect gap wind and barrier jet impacts further east across Southcentral and the north Gulf Coast. This includes Turnagain Arm winds turning into Anchorage on Tuesday as the low lifts north. Southerly onshore flow will keep heavy rain ongoing into the coastal mountains. This includes rain gradually developing south across the Panhandle which will have enjoyed a long stretch of quiet weather under the Pacific High through the weekend. On Tuesday afternoon a strong low (through not nearly as strong as Merbok's remnants) will emerge off of the Kamchatka Peninsula. Its leading front will track eastward along the Aleutian Chain and into the AKPEN by Wednesday afternoon. From there there are significant model differences on how quickly secondary triple-point lows form east of the low. This will determine how quickly the weather deteriorates over the Gulf on Thursday. For now, expect very unsettled weather INVOF the AKPEN and adjacent waters late week. In contrast a reprieve from the more active weather is possible late week for interior areas. The Panhandle is likely to remain unsettled late week, but how unsettled will be highly determined by the eventual track of the low near the AKPEN. Wegman/Hamrick Hazards: - Heavy rain across portions of the coastal southern Alaska and nearby mountainous terrain into the Alaska Panhandle, Tue-Thu, Sep 20-Sep 22. - Heavy rain across portions of mainland Alaska near the southwestern portion of the Brooks Range, Sun, Sep 18. 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