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.
Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact firstname.lastname@example.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.