Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Wed Sep 21 2022 Valid 12Z Sun Sep 25 2022 - 12Z Thu Sep 29 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 middle 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 and high mountain snow. 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 northwestern Gulf. There is also consensus for a polar upper low to slowly drift southward across the northern Bering through Monday. For the next organized storm system emerging across the central and western Aleutians early next week, the GFS has a slightly more southern track with the surface low, and the CMC is indicating a stronger solution as the storm reaches the Alaska Peninsula by Wednesday. By the end of the forecast period, there is still general consensus for a broad upper level gyre over Alaska, although timing and intensity differences are apparent with the low pressure system over the Gulf, with the ECMWF a notably weaker solution. The WPC fronts/pressures are primarily derived from a multi-deterministic blend through Monday, with slightly less weighting to the GFS, and a gradual increase of the ensemble means going into the middle of next week. ...Weather/Hazards Highlights... Heavy rainfall totals are likely across southern portions of the mainland, generally from the eastern side of the Kenai Peninsula to the western southeast Panhandle region going into early next week, associated with atmospheric rivers from multiple fronts. Several inches of rain is expected for lower elevations, particularly where there is terrain enhancement, while high elevations will see heavy snow. Some potential for flooding exists across this region. Elsewhere across the state, periods of rain and breezy conditions are likely for the Aleutians as the next storm system moves through the region around Tuesday and into Wednesday. In terms of temperatures, highs should generally be in the 40s to perhaps low 50s for the lower elevations of the Interior, and near 50 degrees near the southern coastal areas, with a gradual cooling trend going into next week. Highs will likely struggle to get much above freezing for the Arctic Coast. Hamrick Hazards: - Heavy precipitation across portions of southeast mainland Alaska and the Alaska Panhandle, Sat-Wed, Sep 24-Sep 28. 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