What are key words in this? What is a thunderstorm? A thunderstorm is a storm that includes lightning and thunder. Some features of thunderstorms are that they produce strong winds, heavy rain and sometimes hail. Thunderstorms are created when moisture collects to form clouds and rain. Unstable air that is warm and can rise rapidly further aids the process. Finally, lift can form from fronts, sea breezes or mountains to make the perfect environment for a thunderstorm.