Study: Atmospheric River Storms Can Reduce Sierra Snow
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, causing it to melt. 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.
“In California, atmospheric rivers tend to be the warmest winter storms we get. We wanted to understand what the connection was between these storms and rain-on-snow events," said Bin Guan, lead author of the study, which is accepted for publication in the journal Geophysical Research Letters. Guan is affiliated with the Joint Institute for Regional Earth System Science and Engineering, a collaboration between NASA's Jet Propulsion Laboratory in Pasadena, California, and UCLA.
http://www.nasa.gov/feature/jpl/study-atmospheric-river-storms-can-reduce-sierra-snow
