Animation of an atmospheric river storm that occurred on Jan. 28 through 30, bringing half an inch to an inch of rain to many locations in central and southern California. Credit: University of Wisconsin/CIMSS.
NASA March 2, 2016
A new study by NASA and several partners has found that in California’s Sierra Nevada, atmospheric river storms are two-and-a-half times more likely than other types of winter storms to result in destructive “rain-on-snow” events, where rain falls on existing snowpack. Those events increase flood risks in winter and reduce water availability the following summer. The study, based on NASA satellite and ground-based data from 1998 through 2014, is the first to establish a climatological connection between atmospheric river storms and rain-on-snow events. Partnering with NASA on the study were UCLA; Scripps Institution of Oceanography, San Diego; and the Earth System Research Laboratory, Boulder, Colorado. Atmospheric rivers are narrow jets of very humid air that normally originate thousands of miles off the West Coast, in the warm subtropical Pacific Ocean. When the warm, moist air hits the Sierra Nevada and other high mountains, it drops much of its moisture as precipitation. Only 17 percent of West Coast storms are caused by atmospheric rivers, but those storms provide 30 to 50 percent of California’s precipitation and 40 percent of Sierra snowpack, on average. They have also been blamed for more than 80 percent of the state’s major floods….