Thunderstorms form by cumulonimbus clouds that causes the thunderstorm to have heavy rain, gusty winds and sometimes hail. 16 million thunderstorms happen per year. They typically happen in warm weather. Some historical examples of severe thunderstorms are Australian capital territory December 2005-2006 and in Syndey, Australia 1939. Some statistics for thunderstorms is that they average 93 deaths per year. And some of the property damage they do is the winds get so strong that they knock down the trees and the trees land on houses. The 1939 thunderstorm in Sydney, Australia had much more damage than the thunderstorm that happened in 2005-2006. To prepare for a severe thunderstorm you can listen to sirens and you can watch the news for warnings so you cane see how severe the thunderstorm is and how long its going to take before it hits your area.