Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 719 PM EDT Thu Aug 18 2022 Valid 12Z Mon Aug 22 2022 - 12Z Fri Aug 26 2022 ...Generally unsettled weather pattern expected along the Southern Coast and Panhandle next week... ...General Overview... The extended range period over Alaska next week should begin rather amplified and blocky as a deep upper level low stays anchored in place just south of the Alaska Peninsula, and upper level ridging builds across the Bering Sea and into the Mainland. Shortwave energy rounding this upper low will allow for some degree of lingering and reinforced surface low pressure across the Coast and the Gulf through much of next week. 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 an amplified shortwave into the Bering which should work to break down the blockiness and allow for the southern Alaskan low to shift east and upper troughing also making its way into western Alaska by next Friday. ...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. By mid to later next week, the ensemble means, along with the GFS and ECMWF tend to weaken the block allowing for some troughing to move into western Alaska. The 12z CMC, however, maintains a more blocky pattern which allows for the eastern Russia upper low to lift up and north of Alaska and an overall slower translation of troughing into the Bering. This also keeps low pressure just south of the Alaska Peninsula the entire period. There was good enough agreement in the deterministic models the first half of the period for a purely deterministic blend for WPCs forecast today. Given the differences discussed above, opted to incorporate more of the ensemble means days 6 and 7, while still maintaining some of the GFS and ECMWF determinisitic for some added overall system definition. This also maintains good continuity with yesterdays WPC forecast as well. ...Sensible Weather and Potential Hazards... Slow movement of the strong storm system near the Alaska Peninsula is forecast to continue a rather unsettled pattern well into next week across the southern coast and extending into the mountainous terrain of far southern Alaska as well. This blocky pattern may result in 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 teh period, which may lead to some flooding issues. 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. Dependent on evolution of the pattern upstream, rainfall may slowly edge eastward eventually impacting parts of the northern Panhandle by later next week. Precipitation across the rest of Alaska should be mainly light and scattered, although some more enhanced rain could move into western Alaska around next Friday. Surface high pressure over the Arctic should keep North Slope highs near to below normal the first half of next week, though temperatures should trend much warmer by the latter half of the week as the arctic high eventually moves away from the region. 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 areas rather cool during the day as well. Santorelli Hazards: - Heavy rain across portions of mainland Alaska, Mon, Aug 22 and Wed, Aug 24. - Heavy rain across portions of the Alaska Panhandle, 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