Portal:Physics/Selected picture/Week 17, 2007
A thunderstorm, also called an electrical storm, is a form of weather characterized by the presence of lightning and its attendant thunder produced from a cumulonimbus cloud. Thunderstorms are usually accompanied by heavy rainfall and they can also be accompanied by strong winds, hail and tornadoes. In the winter months, snowfall can occasionally take place in a thunderstorm. Such is often termed thundersnow.
Thunderstorms form when significant condensation—resulting in the production of a wide range of water droplets and ice crystals—occurs in an atmosphere that is unstable and supports deep, rapid upward motion. This often occurs in the presence of three conditions: sufficient moisture accumulated in the lower atmosphere, reflected by high temperatures; a significant fall in air temperature with increasing height, known as a steep adiabatic lapse rate; and a force such as mechanical convergence along a cold front to focus the lift. The process to initiate vertical lifting can be caused by (1) unequal warming of the surface of the Earth, (2) orographic lifting due to topographic obstruction of air flow, and (3) dynamic lifting because of the presence of a frontal zone.