It rained in Southern California again on Wednesday.

The storm, Marty Ralph told me, was caused by an atmospheric river, a meteorological phenomenon you have been hearing more about lately as climate change drives bigger swings between tinder dry conditions and pounding rain.

And although the rain caused the usual traffic headaches and advisories against swimming at the beach, this particular atmospheric river was actually “primarily beneficial,” according to a scale that Mr. Ralph, the director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography, helped develop.