And all thunderstorms produce lightning, the weather's second biggest killer in the United States. Thunderstorms Thunderstorms are convective storms that typically occur during the spring and summer months. The process is similar to the convective processes seen when water boils in a pot. The ascending air cools to its dew point and a cloud begins to form from condensation. As water vapor in the upper portions of the cloud becomes supercooled, raindrops begin to form and fall, dragging down cooler air and producing down-drafts.
Updrafts continue to feed warm humid air into the maturing storm cloud.
When down-drafts grow in strength, they eventually choke off the updraft, which starves the storm of its supply of humid air. While the storm is growing, however, cumulus clouds low-level clouds that are often dark on the bottom, with tops resembling a giant white cotton ball expand vertically into monster cumulonimbus clouds. They may appear as single clouds or as part of a wall of an advancing storm system. In either case, they contain large amounts of moisture, including hail. Lightning One of the distinctive side effects of a thunderstorm is lightning, which has played a dominant role in mythology, and is responsible for the deaths of hundreds of people and millions of dollars in property damage each year.