A rapidly rotating column of air
extending vertically from the surface to the base of a cumuliform cloud
, often with near-surface circulating debris/dust
when over land or a spray ring when over water. Although its presence is not required, a funnel cloud
is often visible and may partly or fully extend from the cloud base to the ground.
Characteristics of typical tornadoes include a diameter of 2 km or less, with maximum wind velocity
differences across the circulation exceeding 40 m s−1
within 200 m of the surface. Tornadoes typically last on the order of 100–1000 s. Some may be comprised of multiple subvortices with spatial scales as small as tens of meters, rotating around a central axis. Tornadoes rated by the enhanced Fujita (EF) scale
have wind gusts at 10 m above the surface equaling or exceeding 29 m s−1
(65 mph; the lower bound of EF-0).
Tornadoes that occur over water are classified as waterspouts
are a subset of tornadoes that occur independent of a parent mesocyclone
are not considered tornadoes since they are shallow and short-lived vortices that are usually weak. Dust devils
are not considered tornadoes since they are not associated with cumuliform clouds.
Term edited 16 October 2020.
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