Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 623 PM EDT Tue Aug 16 2022 Valid 12Z Sat Aug 20 2022 - 12Z Wed Aug 24 2022 ***Heavy rain and gusty winds likely for portions of southern Alaska with a persistent low pressure system over the northern Gulf*** ...General Overview... An intensifying surface low currently southwest of the Kamchatka Peninsula will cross the Aleutians over the next few days, and then slow down considerably in its forward progression once it reaches the general vicinity of the Alaska Peninsula, where it is expected to stall this weekend and early next week. This will be the result of a blocky pattern that develops across the state with a ridge axis across western Canada and extending into eastern mainland Alaska. Sustained onshore flow ahead of the low will likely result in prolonged periods of rain from the eastern Aleutians to the Kenai Peninsula, and gusty winds near the coast. ...Guidance/Predictability Assessment... The 12Z guidance continues to strongly agree on a well-defined surface/upper low loitering over the northern Gulf of Alaska this weekend and into early next week, after crossing the Aleutians during the short term period. There has been a slight southward trend in the model consensus with the core of the low generally situated about 100-200 miles south of the Alaska Peninsula for the Sunday through Wednesday time period whilst gradually weakening with time. There is some displacement with the 12Z CMC by keeping the low closer to shore, and the CMC also is displaced farther south with the Arctic surface high during the extended forecast period. In terms of confidence, there is greater overall model spread with shortwave perturbations crossing northern Alaska compared to central and southern portions of the state. The WPC forecast is primarily derived from a multi-deterministic model blend through the weekend, and then focused more on the ECMWF/GFS and their respective ensemble means for Monday-Wednesday of next week. ...Sensible Weather and Potential Hazards... Slow movement of the strong storm system tracking from the Aleutians to the Alaska Peninsula is forecast to produce a rather unsettled pattern over multiple days across the southern coast and extending into the mountainous terrain over the far southern mainland for the weekend and perhaps into early next week. Recent slower trends with the system have delayed arrival of moisture to the southeastern coast and Panhandle, leading to lower amounts over those areas. Some areas along the southern coast may see several inches or more of total precipitation during the period where the atmospheric river becomes established, which may lead to some flooding. This storm will also produce a broad area of brisk to strong winds across the Bering Sea/Aleutians/North Pacific, especially late this week into the weekend. Some areas of precipitation are also possible over the rest of the mainland. Surface high pressure over the Arctic should keep North Slope highs near to below normal for most of the period while clouds and precipitation keep southern areas rather cool during the day as well, with below normal readings extending into at least the northern Panhandle. However, highs may trend to slightly above normal levels over central portions of the mainland. Hamrick Hazards: - Heavy rain across portions of mainland Alaska, Sun-Mon, Aug 21-Aug 22. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon, Aug 22. 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