Waves of heavy rainfall in early December 2025 spurred landslides and flooding in parts of the Pacific Northwest. The deluge was the result of a potent atmospheric river that took aim at the region starting around December 7.
Atmospheric rivers are long, narrow bands of moisture that move like rivers in the sky, transporting water vapor from the tropics toward the poles. They occur around the planet, most often in autumn and winter, with the U.S. West Coast typically affected by moist air that originates near Hawaii. In this event, however, some of the moisture arrived from even farther away, originating roughly 7,000 miles (11,000 kilometers) across the Pacific from 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 GEOS (Goddard Earth Observing System) 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 all the water vapor condensed into liquid. The map’s green areas indicate the highest amounts of moisture. Note that not all precipitable water vapor falls as rain; at least some remains in the atmosphere. Nor is it a cap on how much rain can fall, since rainfall can increase as more moisture flows into a column of air. Still, it serves …