Tornado
Formation, Characteristics, Videos, & Facts
tornado, a small-diameter column of violently rotating air developed within a convective cloud and in contact with the ground. Tornadoes occur most often in association with thunderstorms during the spring and summer in the mid-latitudes of both the Northern and Southern Hemispheres. These whirling atmospheric vortices can generate the strongest winds known on Earth: wind speeds in the range of 500 km (300 miles) per hour have been measured in extreme events. When winds of this magnitude strike a populated area, they can cause fantastic destruction and great loss of life, mainly through injuries from flying debris and collapsing structures. Most tornadoes, however, are comparatively weak events that occur in sparsely populated areas and cause minor damage.
This article describes tornado occurrence and formation as products of instability within the Earth’s air masses and wind systems. Wind speeds and destructiveness are discussed with special reference to the Enhanced Fujita Scale of tornado intensity. For short, descriptive entries on closely related phenomena not covered in this article, see waterspout, whirlwind, and fire storm.
wind speed range**
EF number
metres per second
kilometres per hour
feet per second
miles per hour
*This scale was implemented as the standard scale of tornado intensity for the United States on February 1, 2007.
**Like the Fujita Scale, the Enhanced Fujita Scale is a set of wind estimates (not measurements of wind at the surface). Each level in the Enhanced Fujita Scale is derived from three-second wind gusts estimated at the point of damage to 28 indicators (such as trees, buildings, and various types of infrastructure) and the degree of damage to each indicator. Wind estimates vary with height and exposure. Each value is converted from miles per hour and rounded to the nearest whole number.
Source: Modified from the Enhanced F Scale for Tornado Damage web page (http://www.spc.noaa.gov/efscale/ef-scale.html), produced by the National Oceanic and Atmospheric Association (NOAA).
29–38
105–137
95–125
65–85
1
38–49
138–177
126–161
86–110
2
50–60
179–217
163–198
111–135
3
61–74
219–266
199–242
136–165
4
74–89
267–322
243–293
166–200
5
89+
322+
293+
over 200
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