Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 706 PM EDT Sat Aug 20 2022 Valid 12Z Wed Aug 24 2022 - 12Z Sun Aug 28 2022 ...Unsettled weather to persist across the Gulf Coast of Alaska into next weekend, with periods of heavy rain and strong winds expected... ...General Overview... The extended range period over Alaska next week begins with an upper level low anchored in place just south of the Alaska Peninsula, with upper level ridging across the Bering Sea and into much of the Mainland. Additional shortwave energy rounding the west side of the upper low near the Gulf will amplify as it drops well south of the region, and acts to finally weaken the Gulf low though still keeping some degree of lingering and reinforced surface troughing in the Gulf before it presses east into western North America. Another deep upper level low drifting slowly eastward across eastern Russia will eventually drop into the Bering Sea, skirt western Alaska late next week, with triple point redevelopment again just south of the Peninsula. Sustained onshore flow ahead of the Gulf of Alaska troughs/lows will likely result in prolonged periods of moderate to locally heavy rain from the eastern Aleutians to the northern Panhandle through much of the period, and gusty winds mainly near the coast. ...Guidance/Predictability Assessment... The 12Z guidance today continues to strongly agree on a well-defined surface/upper low lingering near the Gulf of Alaska through Wednesday. There are some typical detail differences to be worked out, especially concerning interaction this system has with another weaker shortwave through the Aleutians at the same time. A general model compromise gives a good starting point for day 4, but after this time the 12z UKMET and CMC are too quick to eject the leftover Gulf troughing eastward and were not used in the blend. By the latter part of next week, the models agree on a deep storm system and cold front moving towards the Bering Sea, though have trended away from significant impacts to western Alaska instead favoring a more southward track over the Peninsula and into the Gulf. The 12z GFS and ECMWF show the best support with the ensemble means for this system, so the late period blend favored the ensemble means with some deterministic incorporation to help with system definition. This approach maintains reasonably good continuity with yesterdays WPC forecast, though with notably less QPF forecast for western Alaska per the latest trends. ...Sensible Weather and Potential Hazards... Multiple storm systems near the Alaska Peninsula and Gulf is forecast to continue a rather unsettled pattern through much of the period across the southern coast, into the mountainous terrain of far southern Alaska, and the northern Panhandle. With the first low, in place when the period begins Wednesday, models continue to indicate an atmospheric river type set-up into the Southern Coast region, with moderate to locally heavy rainfall likely. Several inches of rainfall is possible for some locations along the Southern Coast, which could result in some flooding issues. This storm will also produce a broad area of brisk to strong winds and maritime threats across the same region. After Thursday, the storm should weaken, although general troughing across the Gulf may continue some rainfall, although less intense, across the southern Coast and Panhandle region into next weekend. The next system dropping through the Bering Sea may bring some light rain/winds to western Alaska as early as Thursday-Friday, with another round of moderate to locally heavy rainfall to portions of the southern Coast/northern Panhandle next weekend as the system redevelops in the Gulf. In terms of temperatures across Alaska, upper ridging over the central and northern part of the state should keep highs near or above normal through much of the period, while clouds and precipitation keep southern (and western areas for a time) rather cool during the day as well. Santorelli 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