<P> There are four types of thunderstorms: single - cell, multi-cell cluster, multi-cell lines, and supercells . Supercell thunderstorms are the strongest and most severe . Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes . Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires from the heat generated from the cloud - to - ground lightning that accompanies them . Several means are used to study thunderstorms: weather radar, weather stations, and video photography . Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century . Beyond the Earth's atmosphere, thunderstorms have also been observed on the planets of Jupiter, Saturn, Neptune, and, probably, Venus . </P> <P> Warm air has a lower density than cool air, so warmer air rises upwards and cooler air will settle at the bottom (this effect can be seen with a hot air balloon). Clouds form as relatively warmer air, carrying moisture, rises within cooler air . The moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses . When the moisture condenses, it releases energy known as latent heat of vaporization, which allows the rising packet of air to cool less than the cooler surrounding air continuing the cloud's ascension . If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder . Meteorological indices such as convective available potential energy (CAPE) and the lifted index can be used to assist in determining potential upward vertical development of clouds . Generally, thunderstorms require three conditions to form: </P> <Ol> <Li> Moisture </Li> <Li> An unstable airmass </Li> <Li> A lifting force (heat) </Li> </Ol> <Li> An unstable airmass </Li>

What three conditions are required for thunderstorms to form