Southern California is preparing for a major storm that is expected to bring severe weather conditions starting on Monday. Newsweek reports that the National Weather Service (NWS) has issued warnings for possible tornadoes, winds of up to 60 mph, flash floods, and up to three feet of snow in the mountains. The storm is caused by the merging of two low-pressure systems, creating a rare combination of high levels of water vapor, cold air at high altitudes, and a strong disturbance in the atmosphere.