Aquapedia: What is an “atmospheric river”?
Atmospheric rivers are relatively narrow bands of moisture that ferry precipitation across the Pacific Ocean to the West Coast and are key to California’s water supply…. While atmospheric rivers are necessary to keep California’s water reservoirs full, some of them are dangerous because the extreme rainfall and wind can cause catastrophic flooding and damage. Their presence has been likened to the West Coast version of the hurricane hazard posed to the southeastern United States.