From National Geographic – What is an atmospheric river? “You need two ingredients for an atmospheric river,” says Daniel Swain, a climate scientist at the University of California, Los Angeles. “A plume of really concentrated moisture in the atmosphere and strong, fast winds to move it around.” The concentrated moisture comes from the ocean. Warm oceans evaporate water into the atmosphere, and winds and storms concentrate that water vapor into long, narrow, speedy trains of extra-wet air. Then, big global winds in the lower few miles of the atmosphere accelerate those amped-up, stretched-out, water-rich versions of normal storms. (more)