With tornadoes striking Southern California this week, many are wondering what caused them. The answer lies in a rare hurricane-like storm that slammed the San Francisco Bay Area, and then drifted south to near Monterey Bay instead of heading inland. It drew moist air to Southern California, helping feed the pop-up thunderstorms in the region the following day. Meanwhile, the sun shone brightly earlier in the day around Los Angeles, which heated the ground while cold air entered the area at high altitudes. The resulting temperature contrast created enough atmospheric instability to build the storm that unleashed the Montebello tornado. This tornado was the second to hit Southern California in two days, with over two dozen mobile homes damaged in the first one in Carpinteria. While tornadoes in California are not uncommon, they tend to occur more frequently in winter and spring when powerful storms come ashore.