‘Atmospheric River’ May Put a Dent in California Drought

At long last, a series of Pacific storm systems is producing sorely needed rain and mountain snowfall in California, which has been suffering from one of its worst droughts in at least 500 years.  The storms, which began Thursday and are forecast to last through the weekend, are likely to have their greatest impact in Central and Northern California, including the agricultural powerhouse region that is the San Joaquin Valley.

The storms are tapping into a phenomenon known as an “atmospheric river,” which is a relatively narrow stream of moisture-rich air extending from the tropics northeastward across the Pacific.  Atmospheric rivers have helped end California droughts before, according to research by Michael Dettinger of the U.S. Geological Survey and the Scripps Institution of Oceanography.  Dettinger’s research, which was published in the December issue of the Journal of Hydrometeorology, found that atmospheric river events can effectively end even major droughts in California within just one month.  In fact, Dettinger found that most droughts in the West end abruptly, with one very wet month pulling the state from a significant precipitation deficit to a surplus.

However, California is in such a deep precipitation hole that it would take a statewide average of at least a foot of rainfall to climb out, which forecasters do not see as likely before the end of the wet season on March 31.  In fact, the upcoming storms may just be part of a short-term break in the weather pattern that has favored drought conditions in the West.

‘Atmospheric River’ May Put a Dent in California Drought