Thunderstorms
Thunderstorm, a violent short-lived weather disturbance that is almost always associated with lightning, thunder, dense clouds, heavy rain or hail, and strong winds.
Thunderstorms form when large updrafts of warm moist air rise into the cooler areas of the atmoshere. The moisture in the updrafts condese into massive clouds and eventually come down as percipitation. Cooled air sinks downward creating strong downdrafts and horisontal winds. At the same time, electrical charges accumulate on cloud particles (water droplets and ice). Lightning discharges occur when the accumulated electric charge becomes sufficiently large. Lightning heats the air it passes through so intensely and quickly that shock waves are produced; these shock waves are heard as claps and rolls of thunder. On occasion, severe thunderstorms are accompanied by swirling vortices of air that become concentrated and powerful enough to form tornadoes.
Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes. Thunderstorms are responsible for the development and formation of many severe weather phenomena like tornadoes and lightning. They are rare in polar regions and infrequent at latitudes higher than 50° N and 50° S. The temperate and tropical regions of the world, therefore, are the most prone to thunderstorms. Most of the 2,000 or so thunderstorms occurring at any time in the world are located within the Intertropical Convergence Zone (ITCZ), especially in the afternoon. Abundant tropical moisture, strong surface heating, and vigorous trade-wind convergence are responsible.
Worldwide, there are an estimated 16 million thunderstorms each year, and at any given moment, there are roughly 2,000 thunderstorms in progress. The frequency of thunderstorms varies by location, season and climate.
The duration of a thunderstorm depends on its type and size. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. However, some thunderstorms can last for much longer, especially if they are multicell or supercell storms, which have new updrafts forming along the gust front. These storms can last for many hours and produce severe weather.
Under the right conditions, rainfall from thunderstorms causes flash flooding, killing more people each year than hurricanes, tornadoes or lightning. Lightning is responsible for many fires around the world each year, and causes fatalities. Hail up to the size of tennis balls damages cars and windows, and kills livestock caught out in the open. Strong (up to more than 120 mph) straight-line winds associated with thunderstorms knock down trees, power lines and mobile homes. Tornadoes (with winds up to about 300 mph) can destroy all but the best-built man-made structures.