An atmospheric river dumping rain across Northern California and several feet of snow in the Sierra was making its way across the state Friday, bringing flooding and threatening mudslides along with it. The storm, the first major rainmaker of the season ...

"The average atmospheric river carries an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi," NOAA states.

A major storm with heavy snow and record rain that's moving through Northern California has toppled trees, closed roads and prompted evacuations in some areas after knocking out power to hundreds of thousands of people in Washington and Oregon.