Publication

Tornado - Definition and Facts

26 February 2024

An aerial view of the swirling clouds of the typhoon - DGi

Unique identifier / Notation: MH0059

Synonyms: Twister, Land spout, Cold air funnel, Waterspout, Funnel, Whirlwind.

Type Meteorological and Hydrological

Coordinating agency or organization: World Meteorological Organization (WMO)

A tornado is a rotating column of air, extending from the base of a cumuliform cloud, and often visible as a condensation funnel in contact with the ground, and/or attendant circulating dust or debris cloud at the ground (WMO, 2017).

Primary reference(s)

WMO, 2017. International Cloud Atlas: Tornado. World Meteorological Organization (WMO). Accessed 25 November 2019.

Additional scientific description

A large tornado in which the condensation funnel is at least as wide horizontally at the ground as it is in height from the ground to the cloud base may be referred to as a wedge tornado. During the dissipation stage of a tornado, the condensation funnel will shrink and narrow in width, becoming rope-like (a rope funnel), and may also become contorted. Some tornadoes may contain secondary vortices within the main circulation (suction vortices or subvortices) (WMO, 2017a).

Metrics and numeric limits

Tornadoes can be classified into the following distinct formation groups (WMO, 2017b):

Type I (in association with supercells; WMO, no date),
Type II (in association with quasi-linear convective systems),
and Type III (localised convective and shear vortices – these comprise Landspouts, Waterspouts and Cold-air funnels).

Definitions for the Type III tornados are as follows (WMO, 2017b):

Landspout: A tornado that does not arise from organised storm-scale rotation and is therefore not associated with a wall cloud (murus) or a mesocyclone.
Waterspout: A tornado occurring over water. It is normally a relatively small, weak rotating column of air over open water below a Cumulonimbus or Cumulus congestus cloud.
Cold-air funnel: A funnel cloud or (rarely) a small, relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold.

The strength of a tornado can be estimated from the degree of damage caused using the Enhanced Fujita scale (Wind Science and Engineering Center, 2004; National Weather Service, no date).

Table 21. Enhanced Fujita scale for rating the intensity of tornadoes

Enhanced Fujita scale number	Three second gust speed	Damage
0	29.2−38.1 m/s 105−137 km/h	Minor damage: Tiles blown off or parts of a roof peeled off; damage to gutters or sidings; branches broken off trees; shallow-rooted trees toppled
1	38.3−49.4 m/s 138−178 km/h	Moderate damage: Significant roof damage; windows broken; exterior doors damaged or lost; mobile homes overturned or badly damaged
2	49.7−60.6 m/s 179−218 km/h	Considerable damage: Roofs torn off well-constructed homes; houses moved off their foundations; mobile homes completely destroyed; large trees snapped or uprooted; cars thrown in air
3	60.8−73.9 m/s 219−266 km/h	Severe damage: Entire storeys of well-constructed houses destroyed; significant damage to large buildings; houses with weak foundations blown away; trees begin to lose their bark
4	74.2−89.4 m/s 267−322 km/h	Extreme damage: Well-constructed houses demolished; cars thrown significant distances; top-storey exterior walls of masonry buildings likely collapse
5	>89.4 m/s >322 km/h	Massive/incredible damage: Well-constructed houses swept away; steel-reinforced concrete structures critically damaged; high-rise buildings sustain severe structural damage; trees usually completely debarked, stripped of branches and snapped

Key relevant UN convention / multilateral treaty

Not identified.

Examples of drivers, outcomes and risk management

Owing to the unpredictable nature of tornados, protecting the public is focused on education and outreach which provide information on the tornado as a threat, how to identify a tornado and practical measures on how individuals can protect themselves, and how to find and watch warning systems that alert the public (CDC, 2020).

Since the advent of Doppler Radar, lead times for tornado warnings have increased from when a tornado first touches the ground to upwards of 14 to 20 minutes or more beforehand (WMO, 2017b; National Geographic, 2019).

This article was originally published in the United Nations Office for Disaster Risk Reduction (UNDRR) on this link Tornado | UNDRR (https://www.undrr.org/understanding-disaster-risk/terminology/hips/mh0059)