Tornado

An example of a tornado that hit South Dakota.

A tornado is a violent, rotating column of air that is in contact with both the surface of the earth, and, a cumulonimbus cloud, or, in very rare cases, a cumulus cloud. They are sometimes referred to as twisters or cyclones, but the term "cyclone" is used in meteorology to name any closed low pressure circulation. A tornado can come in many shapes and sizes, but most are in the form of a visible condensation funnel, whose narrow end touches the earth, and is often encircled by a cloud of debris and dust. Typically, tornadoes will have wind speeds less than 110 miles per hour, are about 250 feet across, and travel a few miles, before dissipating. The most extreme tornadoes, however, can attain speeds of more than 300 miles per hour, stretch more than two miles across, and stay on the ground for dozens of miles (sometimes up to 65+ miles)

There are several types of tornadoes, but the most common types are landspouts, waterspouts, or a Multiple vortex tornado. Waterspouts are usually characterized as a spiraling funnel-shaped wind current, connecting to a very large cumulus or a cumulonimbus cloud. Waterspouts are generally classified as non-supercellular tornadoes that develop over the water, although there is disagreement over whether to classify then as real and true tornadoes. These spiraling columns of air frequently develop in tropical areas, which are close to the equator. Waterspouts are less common in high latitudes. Other tornado-like phenomena that exist include the Gustnado, Dust devil, Fire whirls, and Steam devils.

Tornadoes have occurred and have been observed on every continent except Antarctica (however, waterspouts do occur in Antarctica, albeit very rarely). However, most tornadoes in the world occur in the Tornado Alley region of the United States, although they can occur anywhere in North America. Tornadoes have also been known to occasionally occur in south-central and eastern Asia, certain parts of South America, South Africa, almost anywhere in Europe, and some parts of Australia and New Zealand. Certain tornadoes can be detected before, or sometimes as they occur through the use of a Doppler radar.

There are several scales for rating the strength of tornadoes. The Fujita scale rates tornadoes by damaged caused, but certain countries used the Enhanced fujita scale, an updated version of the Fujita scale. The weakest category is an F0 (or EF0) tornado, can damage trees, but not substantial structures. An F5 (or EF5) tornado, which is the strongest category, can rip off buildings off their foundations, and can deform large skyscrapers. Certain countries also use the TORRO scale, where as T0 is an extremely weak tornado, whereas T11 is the most powerful.

Funnel cloud

See Funnel cloud for more information.

A tornado is not necessarily visible, however, the intense low pressure caused by the high wind speeds, and rapid rotation, usually causes water vapor in the air to condense, into cloud droplets due to adiabatic cooling. This will result in the formation of a visible funnel cloud or condensation funnel. Tornadoes often begin as funnel clouds, with no associated strong winds at the surface, and not all funnel clouds evolve into tornadoes. Most tornadoes produce strong winds at the surface, while the visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud, and a tornado from a distance.

Outbreaks

See Tornado outbreak, tornado outbreak sequence, and Tornado family for more information.

Sometimes, a single storm will produce more than one tornado, either simultaneously, or in succession. Multiple tornadoes produced by the same storm cell, however, are referred to as a "tornado family". Several tornadoes are sometimes spawned from the same large-scale storm system. If there is no break in the activity, this is considered a tornado outbreak (although the term "tornado outbreak", can have various definitions). A period of successive days with tornado outbreaks in the same general area (spawned by multiple weather systems) is called a tornado outbreak sequence, which are occasionally called an extended tornado break.

Size and shape

Most tornadoes take the appearance of a narrow funnel, a few hundred yards across, with a small cloud of debris near the ground. Tornadoes might also be obscured completely, by either rain or dust. These tornadoes are especially dangerous, however, as even experienced meteorologists might not see them.

Small, and relatively weak tornadoes may only be visible as a small swirl of dust on the ground. Although the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 40 miles per hour, the circulation is considered a tornado.

A tornado with a nearly cylindrical appearance and a low height can sometimes be referred to as a "stovepipe" tornado. Large single-vortex tornadoes can look like large wedges stuck to the ground, and so are known as "wedge tornadoes", or "wedges". The stovepipe classification can also be used for that type of tornado, if it otherwise fits that profile. A wedge can be so wide, that it appears to be a block of dark clouds, wider than the distance from the cloud base to the ground. Even experienced storm observers might not be able to tell the difference between a low-hanging cloud, and a wedge tornado from a distance. Most, but not all major tornadoes are wedges.

A rope tornado in Alabama.

Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often, curl or twist into complex shapes. These tornadoes can be referred to as a "rope tornado". When they rope out, the length of the funnel increases, which forces the wind within the funnel to weaken. Multiple-vortex tornadoes can appear as a family of swirls, circling a common center, or they may be completely obscured by either condensation, dust, and debris, which makes them appear as a single funnel.

Appearances

Tornadoes can have a wide range of colors, depending on which environment they form in. Those that form in dry environments can be almost invisible, marked only by swirling debris at the base of the funnel. Tornadoes that pick up little or no debris can be gray or white. While traveling over a body of water (as a waterspout tornado), tornadoes can turn very white, and even blue. Slow-moving funnels, which ingest a considerable amount of debris and dirt, are usually much darker, taking on the color of debris. Tornadoes in the Great Plains can be turned red because of the soil, and tornadoes which forum in mountainous areas can travel over snow-covered grounds, turning them white.

Lightning conditions are a major factor in the appearance of any tornado. A tornado which is "back-lit" (a tornado viewed with the sun behind it) will appear very dark. The same tornado, viewed with the sun observer's back, can appear gray or white. Tornadoes which occur near the time of sunset can also be many different colors, which can appear in colors such as yellow, orange, and pink.

Dust that is kicked up by the winds of the parent thunderstorm, heavy rain and hail, and the darkness of night are all factors which can reduce visibility of tornadoes. Tornadoes tat are occurring in these conditions are especially dangerous, since only weather observations, or possibly the sound of the tornado, serve as the warnings to those which are in the storms pass.

Rotation

Tornadoes usually rotate cyclonically. Large-scale storms always rotate cyclonically due to the Coriolis effect.

Types of Tornadoes

Multiple vortex

A multiple vortex tornado.

See Multiple vortex tornado for more information.

A multiple-vortex tornado is a type of tornado, in which two or more columns of spinning air rotate around a common center. Multivortex structure's can occur in almost any circulation, but is very often observed in intense tornadoes. These vortices often create small areas of heavier damage along with the main tornado path. This is a distinct phenomenon from a satellite tornado, which is a weaker tornado which forms very near a large, strong tornado contained within the same mesocyclone. The satellite tornado may appear to "orbit" the larger tornado (which gives it's name "Satellite tornado"), giving the appearance of one, large multi-vortex tornado. However, a satellite tornado is a distinct circulation, and is much smaller than the main funnel.

Waterspout

A waterspout in Lake Michigan on September 29, 2006.

See Waterspout for more information.

A waterspout is defined as a tornado over water. However, researchers typically distinguish fair weather waterspouts from tornadic waterspouts. Fair weather waterspouts are less severe but far more common, and are very similar to dust devils and landspouts. They form over tropical and subtropical waters. They are usually weak tornadoes which travel very slowly. They usually occur over the Florida Keys or the northern Adriatic Sea. In contrast, tornadic waterspouts are stronger tornadoes over water.

Landspout

See Landspout for more information.

A landspout (or a dust-tube tornado) is a tornado not associated with a mesocyclone. The name sterns from their characterization as a "fair weather waterspout on land". Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and more. Landspouts also create a distinctively laminar cloud of dust when they make contact with the ground, due to their differing mechanics from true mesoform tornadoes. Though usually weaker than classic tornadoes, they can produce strong winds, which may cause serious damage.

Other types

Gustnado

See Gustnado for more information.

A gustnado (or gust front tornado), is a small, vertical swirl associated with a gust front or a downburst, hence the name. As they are not connected with a cloud base, there is sometimes debates as to whether or not gustnados are real tornadoes. They are formed when fast moving cold, dry outflow air from a thunderstorm is blown through a mass of stationary, warm moist air near the outflow boundary, resulting in a "rolling effect".

Dust devil

See Dust devil for more information.

A dust devil resembles a tornado in vertical swirling column of air. However, they form under clear skies, and are no stronger than even the weakest tornadoes. They form when a convective updraft is formed near the ground on a hot day. If there is enough low level wind shear, the column of hot, rising air can develop a small cyclonic motion, that can be seen near the ground. They are not considered tornadoes.

Fire whirl

See Fire whirl and Steam devil for more information.

Small-scale, tornado like circulations can occur near any intense surface heat source. Those that occur near intense wildfires are called "fire whirls" (occasionally fire tornado). These are not considered tornadoes, except in a very rare case, where they connect to a pyrocumulus cloud above. Fire whirls usually are not as strong as tornadoes associated with thunderstorms, but they can produce big damage.

Steam devil

See Steam devil for more information.

A steam devil is a rotating updraft that involves steam or smoke. Steam devils are very rare. They most often form from smoke issuing from a power plant's smokestacks. The phenomenon can also occur over water, when cold arctic air passes over relatively warm water.

List of tornadoes

See List of Tornadoes for the main article.