Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 638 PM EDT Tue Sep 26 2023 Valid 12Z Sat Sep 30 2023 - 12Z Wed Oct 04 2023 ...Storm track from south of the Aleutians to the northern Gulf of Alaska to focus impacts from southern to Southeast Alaska this weekend... ...Pattern Overview and Guidance Evaluation/Preferences... The focus during the first half of the period/this weekend will be on a deepening upper low as it moves south of the Aleutians into the Gulf. This should weaken early next week as the energy moves into western Canada but general weak troughing will be maintained over the Gulf and into the Mainland as additional pieces of energy round the western and southern side of an upper low meandering in the Arctic. Upper ridging should build into the Bering Sea and western Alaska next week as another upper low enters the far Western Bering next Wednesday. Recent guidance continues to show very good agreement on the overall upper pattern through the middle of next week, with some typical spread in the details. Details and timing of individual shortwaves rounding the Arctic upper low next week remain in question but are smoothed out by a general model blend. There are some more noticeable timing/placement differences into the Western Bering next week with the next system. The WPC blend for today used a general model blend of the latest 12z guidance through the first half of the period. Transitioned towards a 50/50 deterministic (ECMWF and GFS) and ensemble mean blend by day 8. This maintained good continuity with yesterdays WPC forecast as well. ...Pattern Overview and Weather/Hazards Highlights... The deepening Pacific Storm will track south of the Aleutians into the northern Gulf this weekend, offering possibly significant maritime and coastal high wind/wave threats along with heavy rains. The main impacts will spread across the northern Gulf and inland into the AKPen/Kodiak Island through Southcentral to Southeast Alaska, with models hinting at a possible atmospheric river type set-up. A cold frontal surge in the wake of the 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. Temperatures across Alaska should trend cooler with time, with the greatest anomalies across Southern/Southeast Alaska and the Brooks Range. The North Slope, especially closer to the coast, should stay near or above normal during the period, with western Alaska trending warmer as well by the middle of next week. Santorelli Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Sep 30-Oct 1. 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