Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 645 PM EDT Fri Aug 19 2022 Valid 12Z Tue Aug 23 2022 - 12Z Sat Aug 27 2022 ...Heavy rain and strong winds expected along the Southern Coast of Alaska next week... ...General Overview... The extended range period over Alaska next week begins with a deep upper level low anchored in place just south of the Alaska Peninsula, as upper level ridging builds across the Bering Sea and into the Mainland. Shortwave energy rounding the upper low near the Gulf will allow for some degree of lingering and reinforced surface low pressure along the Southern Coast and the Gulf through into next Thursday. Sustained onshore flow ahead of the low will likely result in prolonged periods of moderate to locally heavy rain from the eastern Aleutians to the northern Panhandle, and gusty winds mainly near the coast. Another deep upper level low drifting slowly eastward across eastern Russia will eventually send amplified troughing into the Bering Sea and western Alaska late next week which should work to weaken the Gulf low and push the leftover troughing into western North America. ...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 at least the first half of next week. Models exhibit some typical timing and intensity differences in the low, but a general model compromise gives a good starting point. By the middle to latter part of next week, the models agree on a deep storm system and cold front to move towards the Bering Sea/western Alaska, but with some more notable timing differences. The 12z CMC stands out as being much slower with the front through the Bering Sea/Aleutians and also with triple point redevelopment near the Alaska Peninsula. The 12z GFS and ECMWF show more support with the ensemble means, so after day 6, the CMC was removed from the blend and replaced with the ensemble means. Continued to incorporate some modest amounts of the mostly agreeable GFS and ECMWF all the way through day 8 to help with system definition. This approach also maintains good continuity with yesterdays WPC forecast. ...Sensible Weather and Potential Hazards... Slow movement of the strong storm system near the Alaska Peninsula and Gulf is forecast to continue a rather unsettled pattern well into next week across the southern coast, into the mountainous terrain of far southern Alaska, and the northern Panhandle. Models continue to indicate an atmospheric river type set-up into the Southern Coast region, with some locations possibly seeing as much as 4 to 8 inches of total rainfall during the period, which may lead to some flooding issues. This storm will also produce a broad area of brisk to strong winds and maritime threats across the same region. The storm system is expected to weaken after Thursday, although general troughing across the Gulf should continue some rainfall, although less intense, across the southern Coast and Panhandle region into next weekend. Elsewhere, the rest of the Alaska should be mostly dry the first half of next week ahead of a strong storm into the Bering Sea. Expect rain and wind impacts to arrive along the West Coast and inland by around Thursday of next week, with some locally heavy rainfall possible. Surface high pressure over the Arctic on Tuesday will lift away allowing for initially much below normal temperatures across the North Slope to trend much warmer by the latter half of the week. Elsewhere, upper ridging over the central part of the state should keep highs near or above normal through next week, while clouds and precipitation keep southern and western areas rather cool during the day as well. Santorelli Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon-Wed, Aug 22-Aug 24. - High winds across portions of mainland Alaska, Wed, Aug 24. 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