The document discusses the formation of major weather events such as tornadoes, explaining that tornadoes require a cold front and low level moisture to form and occur most often in the southern half of the US where more thunderstorms take place, which are necessary for a tornado. It describes how warm, humid air rises quickly in a thunderstorm and can begin to rotate due to wind shear between winds of different speeds and altitudes, potentially tightening into a tornado if caught in the updraft of a supercell storm.