Pacific Moisture Drenches the U.S. Northwest

Waves of heavy rain in early December 2025 caused landslides and flooding in parts of the Pacific Northwest. The flood was the result of a powerful atmospheric river that descended on the region beginning around December 7.

Atmospheric rivers are long, narrow bands of moisture that move like rivers across the sky, carrying water vapor from the tropics to the poles. They occur all over the planet, most commonly in fall and winter, with the west coast of the United States usually affected by humid air from Hawaii. However, in this event, some of the moisture arrived from even further away, coming from about 7,000 miles across the Pacific, near the Philippines.

This map shows the total precipitable water vapor in the atmosphere at 11:30 p.m. Pacific Time on December 10. It is derived from NASA’s Goddard Earth Observing System (GEOS) and uses satellite data and models of physical processes to approximate what is happening in the atmosphere.

Precipitable water vapor represents the amount of water contained in a column of air, assuming that all the water vapor is condensed to liquid. Green areas on the map indicate the highest humidity levels. Note that not all precipitable water vapor falls as rain; at least part of it remains in the atmosphere. This is also not a limit on the amount of rain that can fall, since precipitation can increase as more moisture flows through an air column. Nevertheless, it is a useful indicator of areas where excessive precipitation is likely.

According to the National Weather Service, preliminary ground measurements showed that several locations in western Washington received more than 10 inches (250 millimeters) of rain over a 72-hour period ending the morning of Dec. 11. Seattle-Tacoma International Airport set a record for daily precipitation on Dec. 10, with 1.6 inches (40 millimeters).

River flooding continued on December 11, with the Skagit and Snohomish rivers experiencing record or near record flood levels that day. Floodwaters and mudslides closed many roads, including the eastbound lanes of I-90 in western Washington.

NASA’s Disaster Response Coordination System has been activated to support the Washington State Emergency Operations Center’s ongoing response efforts. The team will publish maps and data products on its open access mapping portal as new information becomes available.

NASA Earth Observatory images by Lauren Dauphin, using GEOS data from NASA GSFC’s Global Modeling and Assimilation Office. Story by Kathryn Hansen.

• Cliff Mass Weather Blog (December 8, 2025) The torrent has begun: the Filipino connection. Accessed December 11, 2025.
• National Water Center, via X (December 10, 2025) Key messages for Pacific Northwest flooding. Accessed December 11, 2025.
• National Weather Service (December 11, 2025) Miscellaneous Hydrologic Data. Accessed December 11, 2025.
• NOAA (February 21, 2025) What are atmospheric rivers? Accessed December 11, 2025.
• The United States today (December 11, 2025) Catastrophic flooding triggers evacuations in Washington state. See forecast. Accessed December 11, 2025.
• The Washington Post (December 8, 2025) A 7,000-mile atmospheric river stretches from the Philippines to the United States. Accessed December 11, 2025.