An atmospheric disturbance involving perturbations of the prevailing pressure and wind fields on scales ranging from tornadoes (1 km across) to extratropical cyclones (2,000-3,000 km across) which may be accompanied by rain, blizzard, lightning and related phenomena, and preceded or accompanied by squalls. Storms may: cause flooding and damage to crops; uproot trees; damage roofs and chimneys; break windows, leading to rain damage; overturn trucks; affect transportation, communication and energy supplies; delay building construction; and destroy traditional landmarks. In their more violent form, storms may cause severe damage and loss of life.
It has been estimated that approximately 1,800 thunderstorms are active over the world at any one time. Over the period 1970-81, 353,832 persons were killed, and property worth 12,600 million dollars damaged by storms. Early in 1990 in Europe, over a period of 6 weeks, 5 storms killed nearly 200 people and caused over $11 billion damages. Large storms of increasing intensity and frequency are expected by some climatologists as a result of the greenhouse effect, since more heat provides greater energy for storms.