A mature cumulonimbus, or thunderstorm, cloud produces rain and hail on the Great Plains. The hail core is evident in the bright white streaks (center). Thunderstorms form as the moisture in updrafts-rapidly rising, warm air-condenses into raindrops or hail. As the updrafts rise through the cloud and into noticeably warmer air, the top of the cloud spreads out and flattens (top). Rain and hail start to fall when the updrafts no longer have the energy to carry the heavy precipitation. Thunderstorms can last from one to several hours.