Five regional events were considered “extreme,” including an atmospheric river that ripped through western Washington in December 2025.
SEATTLE — The Center for Western Weather and Water Extremes released an update on atmospheric rivers Tuesday, highlighting impacts felt along the West Coast through parts of 2025 and 2026.
Most of the annual rainfall across the studied area fell in the “weak” to “moderate” category.
Five regional events were considered “extreme,” including an atmospheric river that ripped through western Washington in December 2025, triggering historic floods.
Forty-five atmospheric rivers in total impacted Washington state in the recent “water year,” a form of timekeeping that usually begins Oct. 1 and ultimately concludes Sept. 30 of the following calendar year.
Washington and Oregon were the most impacted regions, with northern California coming in third, followed by central and southern parts of the Golden State.
The Center for Western Weather and Water Extremes was founded in 2014 to research atmospheric rivers and their impact on the West Coast.
An example of the organization’s research includes the flying of a special class of plane inside an atmospheric river to determine its strength.
The group has also studied recent record-breaking heat over the western U.S., partially caused by an atmospheric river that built an upper-level ridge and surface high pressure system.
Atmospheric rivers typically occur between October and March, so the current water year is not expected to see a substantial increase beyond its 45 count.
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