Alaska Extended Forecast Discussion National Weather Service College Park MD 607 PM EDT Fri Aug 22 2025 Valid 12Z Tue 26 Aug 2025 - 12Z Sat 30 Aug 2025 ...Multi-day heavy rain/flooding and wind threat for the Mainland extending well into next week as fueled by an atmospheric river with a tropical connection... ...Guidance Evaluation/Preferences... The 12 UTC GFS/ECMWF/UKMET/Canadian model solutions seem well clustered valid for Tuesday/Wednesday in an energetic pattern with above normal predictability. A composite maintains good WPC product continuity and has good ensemble support. The 12 UTC GFS then ejects an anchoring closed upper low/trough position eastward over the Arctic Ocean mid-later next week more than other guidance, a recent bias for blocky high latitude systems with some runs of the GFS. Accordingly, instead prefer a blend of more compatible guidance of the 12 UTC ECMWF/Canadian models and the GEFS/ECMWF/NAEFS ensemble mean at these longer time frames. Even so, all guidance tends to offer reasonably similar flow evolutions over the full forecast domain, bolstering confidence. ...Weather/Hazards Highlights... Expect a deep, closed upper low/trough position will remain anchored over the Arctic Ocean well into next week as a mid- upper latitude closed upper low/trough slowly loses influence over the Gulf of Alaska/Northeast Pacific as a maritime hazard. In between, a long fetch of deep moisture and a pooling wavy frontal system/supporting main upper trough shift over the Aleutians and the Bering Sea to take aim on Western/Southwestern Alaska into early/mid next week, with multi-day rainfall/flooding and wind threats over coastal areas spreading broadly inland into the Interior also affecting the Brooks and Alaska Ranges. This well established atmospheric river has connection to current west Pacific Tropical Depression Lingling. Activity may be further enhanced and protracted as shortwave energy rotates through the southern periphery of the Arctic Ocean closed low. The trajectory/axis of the heavy rain will slowly become orientated more Southwest-Northeast over Southwest/west-central portions of the state before slowly shifting transitional focus to the Alaska Peninsula, Kodiak Island then SouthCentral Alaska/Alaska Range with downstream translation of the supporting closed upper trough and deepened surface low/system foray into Gulf waters into mid- later next week. There is an emerging threat for an inland surge of high winds and terrain enhancing gap flows to monitor. More details about threat focus can be found on the WPC Hazards Outlook. Schichtel 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