Summary (tl;dr)

The Pacific Northwest is currently experiencing severe weather due to an unusually long and intense atmospheric river, leading to widespread flood warnings, heavy rainfall, and an increased risk of landslides in areas including Seattle and Portland.

Essential Background

Atmospheric rivers are narrow corridors of concentrated moisture in the atmosphere, often transporting significant amounts of water vapor from the tropics to higher latitudes. While they are a common weather phenomenon in the Pacific Northwest during fall and winter, the current event involves an exceptionally long atmospheric river, stretching an estimated 7,000 miles from the Philippines across the Pacific Ocean. Prior rainfall has already saturated soils in the region, increasing the susceptibility to flooding and landslides.

The Full Story

A powerful atmospheric river began impacting the Pacific Northwest on Monday, December 8, 2025, bringing several days of heavy rain, strong winds, and the threat of extensive flooding. Forecasters predict that the amount of moisture carried by this atmospheric river, rated as Category 4 or 5 on the Center for Western Weather and Water Extremes' scale, could break December rainfall records in parts of central and western Washington. Flood watches and warnings have been issued across western Washington and Oregon, including the metropolitan areas of Seattle and Portland, valid through Friday, December 12. Rainfall totals could exceed a foot in the hardest-hit areas, particularly on the western slopes of the Cascades, with cities like Seattle and Portland expected to receive several inches. Major rivers such as the Skagit, Skykomish, Snoqualmie, Puyallup, Nisqually, and Cowlitz in Washington, and the Willamette and Clackamas rivers in Oregon, are anticipated to reach or exceed major flood stages. The combination of saturated soils and heavy precipitation also significantly elevates the risk of landslides and debris flows, especially in steep terrain and burn-scar areas. Gusty winds up to 45 mph are accompanying the storms, raising concerns about downed trees and power outages.

Why It Matters

This prolonged and intense atmospheric river event carries significant implications for the Pacific Northwest. The potential for widespread and major flooding poses a direct threat to infrastructure, homes, and public safety, with the risk of extensive inundation of structures and roads. The heightened danger of landslides and debris flows could further endanger communities, particularly those in vulnerable areas. Such extreme weather events are historically linked to substantial economic costs, with atmospheric rivers contributing to 80% of all flooding damage on the West Coast, amounting to approximately $1 billion annually. Residents are urged to stay informed about local advisories and prepare for potential disruptions, including power outages and difficult travel conditions.

Geographic Location

• Seattle, King County, Washington, United States (heavy rain, urban and river flooding, landslide risk, coastal flooding, wind advisory)
• Portland, Multnomah County, Oregon, United States (heavy rain, urban and river flooding, landslide risk, wind advisory)
• Snohomish County, Washington, United States (river and stream flooding, wind advisory)
• Western Washington, Washington, United States (widespread flood watches, rising river levels on Skagit, Skykomish, Snoqualmie, Puyallup, Nisqually, and Cowlitz rivers, landslides)
• Northwest Oregon, Oregon, United States (widespread flood watches, rising Willamette and Clackamas rivers, landslides)
• Olympic Peninsula, Washington, United States (heavy rain, rising rivers)
• Cascade Mountains, Washington, United States (heavy rain, high-elevation snow, rising river levels)
• Cascade Mountains, Oregon, United States (heavy rain, rising river levels)
• Northern Idaho, Idaho, United States (heavy rain and potential flooding)
• Western British Columbia, Canada (significant rainfall, high-elevation snow, strong winds)