Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 609 PM EDT Mon Sep 25 2023 Valid 12Z Fri Sep 29 2023 - 12Z Tue Oct 03 2023 â€Storm track from south of the Aleutians to the northern Gulf of Alaska to focus impacts from southern to Southeast Alaska this weekend†...Guidance Evaluation/Preferences... Recent forecast spread and run to run continuity model issues may be gradually easing, but remain problematic enough to still lend preference for this Friday through next Tuesday for a composite of better clustered 12 UTC GEFS/NAEFS/ECMWF ensemble means along with added manual adjustments. WPC product continuity is best maintained in this manner. Guidance differs by the weekend with the digging of Arctic stream energies through the Interior and any extent of later phasing with energies over the Gulf of Alaska. The ensemble mean blend offers moderately amplified upper flow amplitude and interaction supportive of unsettled weather along with colder temperatures for much of the mainland. Meanwhile, there is growing support for development of a threatening storm track from south of Aleutians to the northern Gulf of Alaska late week through the weekend, with main impacts from southern to Southeast Alaska. The ensemble mean track and timing remains between 12 UTC GFS/ECMWF guidance. Manual adjustments were applied to ensure a deepened storm given support, offsetting the blending process and to best fit stronger model trends. ...Pattern Overview and Weather/Hazards Highlights... Flow wrapping around a leading/lifting Bering Sea to western Alaskan low pressure system should fuel light to moderate precipitation from western and northwest Alaska inland through the Interior to the Brooks Range and North Slope into Friday, along with broad overall unsettled flow that should linger this weekend with addition of uncertain Arctic stream upper trough energies, but likely cold frontal passage down through much of the mainland. Meanwhile, the forecast signal continues to grow in support of development and track of a deepening Pacific storm system from south of the Aleutians to the northern Gulf of Alaska late week through the weekend. This storm still offers some uncertainty, but should offer progressive but intense maritime and coastal high wind/wave threats along with wrapping heavy rains. Main impacts will spread across the northern Gulf of Alaska and inland into the AKpen/Kodiak Island through Southcentral to Southeast Alaska through next weekend. The aforementioned cold frontal surge in the wake of main system passage, as aided by northern stream flow, may also then set the stage for enhanced gap wind flow through Southcentral Alaska and vicinity that will need to be monitored later weekend into early next week. Schichtel Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat, Sep 30. 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