In recent years, "atmospheric river" has become used much more frequently in scientific papers and in media coverage. According to experts who study climate and weather, a few reasons may explain why.
The National Weather Service warns the storm could drop unprecedented rain over a wide area from Saturday night through early next week, with the period of most concern from Sunday into early Monday.
An atmospheric river is a relatively narrow channel of wind, hence the "river," that transports water vapor from the tropics to the West Coast, where it's producing rain and heavy winds.