The storm currently hitting Southern California is the second this week, but it’s far different than its predecessor. The earlier storm originated near Alaska, like many of California’s winter storms do, but it packed little rain because it tracked over land instead of the Pacific Ocean. The second storm, the one that began drenching the region Thursday, is what’s known as an atmospheric river. It’s a type of storm that begins far out at sea, allowing it to gather abundant moisture as it barrels toward land driven by high winds.