Alaska Extended Forecast Discussion National Weather Service College Park MD 604 PM EDT Sat Aug 23 2025 Valid 12Z Wed 27 Aug 2025 - 12Z Sun 31 Aug 2025 ...Multi-system heavy rain/flooding/wind threats for Alaska this week fueled by an atmospheric river with a tropical connection... ...Guidance Evaluation/Preferences... 12 UTC GEFS/ECMWF/Canadian ensemble mean solutions seem very well clustered through medium range time scales. This portends pattern evolution and hazards signals with above normal predictability despite some growth trend in deterministic model forecast spread of embedded systems. A composite is favored coupled with manually applied adjustments to ensur sufficient surface system strength otherwise limited by the blending process. This maintains good WPC product continuity. ...Weather/Hazards Highlights... What has proven to be a persistent closed upper low/trough position over the Arctic Ocean to the north of the state should linger well into next week as a pesky mid-upper latitude closed upper low/trough loses influence over the Gulf of Alaska/Northeast Pacific. In between, a long fetch of deep moisture and a pooling wavy frontal system/supporting main upper trough position shift over the Aleutians/Bering Sea will take aim on West/Southwest Alaska through at least next midweek, with multi- day rainfall/flooding and wind threats over coastal areas spreading broadly inland into the Interior to also affect portions of the Brooks and Alaska Ranges. This well established atmospheric river has some connection to the tropical West Pacific. Activity may be further enhanced and protracted as shortwave energy rotates through the southern periphery of the Arctic Ocean closed low. A main axis of heavy rain chances will pivot to become orientated more Southwest-Northeast over Southwest/west-central portions of the state. Energy and moisture will become more focused later next week into the Alaska Peninsula and Kodiak Island, and then especially with the potential for very heavy rainfall potential into SouthCentral Alaska, with additional wet flow into the Alaska Range, both with downstream translation of the supporting closed upper low/trough and deepened surface low/system and triplepoint low foray into Gulf waters into mid- later next week. There is an emerging threat for a surge of high winds into coastal areas/waterways and farther inland into terrain enhancing gap flows to monitor. More details about threat focus can be found on the WPC Hazards Outlook as now produced daily 7X week (linked below). Upstream...there is quite a growing signal to highlight development and track of a deep storm across the Aleutians and into southern Bering Sea heading into next weekend that will pack high winds and waves and enhanced wrapping rains. This will be a maritime threat slated to increasingly affect the Mainland later next weekend. 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