The Cordell, Oklahoma, tornado of May 22, 1981. Source: National Severe Storms Laboratory/University of Mississippi Tornado Intercept Project.
A tornado is the most violent kind of storm. It is an intense whirlwind of small diameter, extending downward from a convective cloud in a severe thunderstorm, and generally funnel-shaped cloud. Air rises rapidly in the outer region of the funnel, but descends in its core, which is at very low pressure. The funnel is visible owing to the formation of cloud droplets by expansional cooling in this low pressure region. Very high winds spiral in toward the core. These, and explosions due to the low pressure, account for the almost total devastation and loss of life in the path of the tornado – which itself might move at up to 200 m/s.
Though generally rare, tornadoes occur worldwide, especially in the US and Australia in spring and early summer. When they occur over water, they give rise to a waterspouts.