A thunderstorm is one of a the most dramatic events that occurs in the atmosphere. Storms are more likely to happen when the air is warm and humid and usually last for one or two hours. They begin when large cumulus (thunder clouds) from in the sky. Lightning flashes are caused by the electicity which builds up in a thunder cloud. Lightning can travel from cloud to cloud as well as from cloud to ground. The noise of thunder is caused by the rapid expansion of air heated by the flash of lightning to a temperature five times hotter than that of the Sun. Thunder and lightning happen at the same time but, because light travels faster than sound, we see the lightning before we hear the thunder when we are some distance from the storm. A VERY NOISY PLACE; Bogor, in Java, has had as many as 322 thundery days in one year. It usually has about 215 days when thunderstorms occur. IN A NOISY WORLD; The world has about sixteen million thunderstorms each year.