A rare tornado touched down near Los Angeles on Wednesday. It followed another major storm that hit the state of California on Tuesday. The violent weather brought heavy rain and snow from the Pacific Ocean. It caused floods, moved earth, uprooted trees, and forced thousands of Californians to leave their homes. The National Weather Service said Tuesday’s storm was a weather system connected to the 12th so-called atmospheric river since late December. Atmospheric rivers are long and wide areas, like a river, of water vapor in the atmosphere that forms over an ocean. The National Oceanic and Atmospheric Administration says these weather systems carry as much water vapor as the average flow of water at the mouth of the Mississippi River. When atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow. Atmospheric rivers come in many shapes and sizes. The largest of those can create strong winds and can cause extreme rainfall and floods. They can cause large amounts of damage to property and life. But atmospheric rivers are an important part of the world’s water cycle. In the western part of the United States, they bring snow to the Sierra Mountains in the winter. The snow then melts and releases water in the spring and summer for power, farming, and drinking water for millions of people.