Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 700 PM EDT Wed Sep 07 2022 Valid 12Z Sun Sep 11 2022 - 12Z Thu Sep 15 2022 ...Heavy rain threat for parts of southern and southeast Alaska early next week... ...Pattern Overview and Guidance/Predictability Assessment... The extended range period over Alaska (Sunday-Thursday) features a weakening initial shortwave trough/surface front in the Gulf, with an upper low becoming established across the Bering this weekend. The energy in the Bering should eventually shift into the Gulf by mid-next week resulting in a surface low pressure system again impacting parts of southern and southeast Alaska. Some form of amplified troughing should maintain across the Gulf through day 8, as upper level ridging builds across the central/eastern Aleutians and Peninsula in response to a an upper low entering the domain by day 7/Wednesday. Models suggest this low pressure system may rapidly deepen as it reaches the far western Aleutians by Wednesday and into the Bering Sea on Thursday. The 12z guidance suite for today shows overall good agreement on this large scale pattern especially the first half of the period, although with plenty of lingering differences in the details and timing of individual systems. A general model blend seemed to suffice for the days 4-6 period. Some greater uncertainties in timing begin to arise with the deepening low towards the Aleutians at the end of the period, although there is good agreement that this system could be modestly strong with many solutions suggesting central low pressure near or below 970mb by next Thursday. Given the increased timing and detail uncertainties, the WPC forecast leaned a little more on the ensemble means for days 7-8. Did continue to include at least half of the deterministic solutions though for some added system definition and strength to the late period Aleutians low. Generally, this maintains good continuity with the previous WPC forecast as well. ...Sensible Weather and Potential Hazards... The main emphasis of the forecast going into the weekend will be the evolution of a couple of shortwaves digging from the Bering into the Gulf, which should keep portions of southern and southeast Alaska rather wet and unsettled through the period. Onshore winds ahead of an occluded cyclone initially in the Bering Sea on Sunday will transport moisture and help focus several days of rainfall, heavy at times, along the southern Coast and points inland, with some snow in the higher elevations. Moisture should reach into portions of western Alaska as well, mainly on Sunday. By Tuesday, low pressure should redevelop in the Gulf of Alaska which should act to enhance the rainfall and expand it eastward into southeast Alaska and northern portions of the Panhandle Tuesday and Wednesday. Multi-day totals of 3 to 4+ inches is possible in this region. Meanwhile, a rapidly deepening cyclone towards the Aleutians next Wednesday will likely bring an increased chance of rain, winds, and maritime threats across much of the Aleutians into Thursday. Temperatures across the southern half of Alaska should remain near or below normal as clouds and precipitation dominate, while a warming trend looks to be on tap for the North Slope region and eastern Alaska. Santorelli Hazards: - Heavy rain across portions of coastal southern Alaska, Sun-Wed, Sep 11-Sep 14. - Heavy rain across portions of coastal southern Alaska into the Alaskan Panhandle, Tue-Wed, Sep 13-Sep 14. 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