Alaska Extended Forecast Discussion National Weather Service College Park MD 550 PM EDT Sun Aug 24 2025 Valid 12Z Thu 28 Aug 2025 - 12Z Mon 01 Sep 2025 ...Multi-system heavy rain/flooding/wind threats for Alaska this week fueled by an atmospheric river with a tropical connection... ...Guidance Evaluation/Preferences... The 12 UTC GEFS/ECMWF/Canadian ensemble mean solutions again 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. An ensemble mean composite is favored coupled with manually applied adjustments to ensure sufficient surface system strength otherwise limited by the blending process. This maintains great WPC product continuity. ...Weather/Hazards Highlights... A persistent closed upper low/trough position over the Arctic Ocean should finally weaken this week as another closed upper low/trough loses influence over the far southeast Gulf of Alaska/northeast Pacific. In between, a long fetch of deep moisture and a pooling wavy frontal system/supporting main upper trough position shifts over the Aleutians/Bering Sea. Aim will remain on West/Southwest Alaska through mid-later week, with multi-day rainfall/flooding and wind threats over coastal areas spreading inland into the Interior to also focus into western portions of Brooks and Alaska Ranges terrain. a well established atmospheric river has connection to the tropical West Pacific. Activity may be further enhanced early period 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 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 This is both with downstream translation of the supporting closed upper low/trough and deepened surface low/system and triplepoint low foray into Gulf waters. 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 remains a strong signal to highlight development and track of a deep storm across the Aleutians into southern to southeast Bering Sea heading into next weekend that looks to offer wrapping high winds/waves and heavy rain threats given another long fetch moisture connection. This protracted maritime threat should also steadily work downstream to support another round of impactful weather with wind/rain threat focus from Southwest Alaska and the Alaska Peninsula/Kodiak Island into SouthCentral Alaska with transition from August into September. 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