Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Tue Sep 20 2022 Valid 12Z Sat Sep 24 2022 - 12Z Wed Sep 28 2022 ***Periodic heavy precipitation is likely this weekend into early next week across the southeastern mainland and Panhandle*** ...Synoptic Overview... A rather unsettled weather pattern will likely be in place across Alaska and adjacent coastal waters for the upcoming weekend and into the first half of next week, with an amplified upper level trough with multiple embedded impulses remaining entrenched over the region. This will particularly be the case across the southern coastal areas and into the southeast Panhandle, where multiple storm systems over the Gulf will lead periods of rain. A building upper level ridge over western Canada and the northwest U.S. will act to serve as a bit of a block and limit the eastward progression of the low pressure systems. ...Guidance/Predictability Assessment... The 12Z model guidance suite depicts good overall synoptic scale agreement for the upcoming weekend across the Alaska domain, and all favor an amplified trough over the Alaska Peninsula and the northern Gulf. There is also consensus for a polar upper low to slowly drift westward just north of the Bering Strait through Sunday. Going into early next week, the GFS becomes faster and a bit more amplified with the pivoting trough axis across the Gulf region, and there remains considerable placement differences on the eventual location of a developing triple point low. With the next impulse arriving across the Aleutians, the ECMWF is slightly slower than the GFS/CMC, but still has enough ensemble support to be incorporated into the forecast. The WPC fronts/pressures are primarily derived from a multi-deterministic blend through Sunday, with slightly less weighting to the GFS, and a gradual increase of the ensemble means going into early next week. ...Weather/Hazards Highlights... With a steady stream of moisture directed towards the southeastern part of the state, heavy rainfall totals are likely, generally from the eastern side of the Kenai Peninsula across the southeastern mainland and through the Panhandle region going into early next week, associated with atmospheric rivers with multiple fronts. Rain is expected for lower elevations while high elevations will see heavy snow. While there are some model discrepancies for the details of exactly where precipitation will be the heaviest, the pattern is favorable for enhanced totals. Then as another low pressure system moves near and possibly across the Aleutians early next week, this could provide some focus for precipitation there as well. The forecast pattern with the upper low aloft will support below average high temperatures across the southern mainland and Panhandle through the period, while central/northern parts of the mainland should see at least a mix of above/below normal highs on most days. Hamrick 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 Hazards: - Heavy precipitation across portions of southeast mainland Alaska and the Alaska Panhandle, Fri-Tue, Sep 23-Sep 27. 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