Damaging winds and heavy rains in California have knocked out power to tens of thousands, caused flash flooding and contributed to the deaths of at least two people. Authorities warned residents Thursday to hunker down at home in anticipation of flooded roads, toppled trees and other risks. The storm is the latest in a series of what are known as atmospheric rivers to hit California. Those are long plumes of moisture stretching far over the Pacific. This one was a so-called Pineapple Express originating near Hawaii and pulled toward the West Coast by a rotating area of rapidly falling air pressure known as a bomb cyclone.

Another round of widespread rain and heavy snow in the mountains is shaping up for recently drenched California and much of Nevada in the comi…