Thunderstorms need three elements in order to form. One of these elements is moisture. The second element is rapidly rising, warm and unstable air. The third element is lifting, commonly produced from fronts and mountains.
The action of warm air rising up and cold air sinking down is a key factor in the formation of thunderstorms. When warm, humid air that is saturated with moisture is forced to rise quickly due to high temperatures, thunderstorms begin to form. The puffy clouds in the sky, known as cumulus clouds, form the same way thunderstorms do. When warm, humid air rises, it begins to expand and cool. This warm air eventually cools to the point that the moisture forms water droplets, and it releases heat into the surrounding atmosphere. This released heat, in turn, causes the rising air mass to increase the rate at which it rises. As the upward movement continues, more moisture is condensed from the air mass, and the droplets come together to form what is known as a rain cloud. Depending on the conditions in the atmosphere, this rain cloud continues to rise as high as 6 to 9 miles into the air. As the cloud grows, more and more moisture condenses and clings to the droplets. The droplets produce small amounts of friction by rubbing or bumping into each other. The result of this friction is lightning and thunder. The droplets continue to grow as long as they can be supported by the updrafts occurring. Once the droplets become too heavy to be supported by the updrafts, they fall from the cloud in the form of rain.