Massive Atmospheric River Hits Pacific Northwest

In early December 2025, the Pacific Northwest experienced severe flooding and landslides due to a powerful atmospheric river that began impacting the region around December 7. This weather phenomenon, characterized by narrow bands of moisture, transported water vapor from as far as 7,000 miles away, originating near the Philippines.

A map from NASA's Goddard Earth Observing System (GEOS) indicated significant levels of precipitable water vapor in the atmosphere, suggesting conditions ripe for excessive rainfall. Preliminary reports from the National Weather Service indicated that western Washington received over 10 inches (250 millimeters) of rain within a 72-hour period, with Seattle-Tacoma International Airport recording a daily rainfall record of 1.6 inches (40 millimeters) on December 10.

As a result of the heavy rainfall, river levels surged, leading to record or near-record flooding in the Skagit and Snohomish Rivers. Numerous roadways, including I-90, faced closures due to floodwaters and mudslides. In response to the crisis, NASA's Disasters Response Coordination System was activated to assist the Washington State Emergency Operations Center, providing maps and data to support ongoing emergency efforts.

This event underscores the increasing frequency and intensity of atmospheric rivers, which are becoming more common during the autumn and winter months along the U.S. West Coast.