Convective clouds that succeed in producing lightning are thunderstorms by definition. A rather wide range of convective conditions satisfy this definition. The most violent convective clouds in the atmosphere, with vertical air motions of many tens of meters per second, are invariably thunderstorms and usually exhibit frequent lightning. In other situations gentle convection with vertical motions of tens of centimeters per second can occasionally attain thunderstorm status. Thunderstorms are a major source of global precipitation and by virtue of their vertical mass transport are major players in determining the distribution of water substance throughout the atmosphere.