Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 705 PM EDT Thu Sep 08 2022 Valid 12Z Mon Sep 12 2022 - 12Z Fri Sep 16 2022 ...Heavy rain threat for parts of southern Alaska and parts of the Panhandle early to mid next week... ...Pattern Overview and Guidance/Predictability Assessment... The extended range period over Alaska begins Monday with a deep upper level low/surface cyclone in the Bering Sea, which will translate into the Gulf by Wednesday. Upper level ridging should then build back across the Aleutians/Bering Sea in response to an upper low entering the domain by day 6/Wednesday. Models suggest this low pressure system may rapidly deepen as it reaches the far western Aleutians and moves into the Bering Sea Thursday/Friday. The 12z guidance suite for today continues to show overall good agreement on this large scale pattern, although with plenty of lingering differences in the details and timing of individual systems. There are some initial timing differences as the initial shortwave moves into the Gulf on Tuesday, but a general model blend for days 4-6 seems to mitigate this enough and create a reasonable starting point. The next deepening low towards the Aleutians later in the week offers significantly more uncertainty as some of the deterministic guidance shows multiple low centers and disagree of which of those may become dominant. There is good agreement that this low eventually ends up (somewhere) in the Bering by day 8/Friday but the track of which it takes is unsure. Given the low confidence, opted to stick close to the ensemble means for now, which offers a nice middle ground and less chaotic solution/track, bringing the low center close to the western coast of Alaska by late next week. Did maintain some smaller contributions from the deterministic ECMWF and CMC which are the closest to the ensemble means. This allowed for some additional manual deepening on the low pressure from the normally weaker ensembles means. This also maintains very 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/cyclones digging from the Bering into the Gulf, which should keep much of southern and southeast Alaska and into the Panhandle rather wet and unsettled through most of the period. Onshore winds ahead of an occluded cyclone and cold front moving through the Aleutians and into the Gulf 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. Multi-day rainfall totals of 3 to 4+ inches are possible in this region. Heaviest rainfall then should move towards the Panhandle, with a lull mid to late next week across the southern Coast in between systems. Meanwhile, the next system towards the Aleutians offers an increased chance of rain, winds, and maritime threats across much of the Aleutians into Thursday, with some precip also likely to begin impacting western Alaska late next week as well. Santorelli Hazards: - Heavy rain across portions of coastal southern Alaska, Sun-Tue, Sep 11-Sep 13. - Heavy rain across portions of coastal southern Alaska into the Alaska 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