Tornado

A tornado, also known as a twister, is a rapidly rotating column of air that stretches from the surface of the Earth up to the base of a cumulonimbus or cumulus cloud. Tornadoes are often, but not always, visible as a condensation funnel reaching down from the cloud base, and a cloud of spinning debris and dust often forms near the ground. For news about the current tornado season, see Tornadoes of 2026. For other uses of the word, see Tornado (disambiguation).

Most tornadoes have wind speeds below 180 kilometers per hour (110 miles per hour). They are about 80 meters (250 feet) wide and usually travel a few kilometers (a few miles) before fading away. The most extreme tornadoes can reach wind speeds above 480 kilometers per hour (300 mph). Some are more than 3 kilometers (2 miles) across and can stay on the ground for more than 100 kilometers (62 miles).

There are several types of tornadoes, including the multiple-vortex tornado, the landspout, and the waterspout. Waterspouts are spiraling, funnel-shaped columns of wind that connect to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that form over bodies of water, although scientists disagree about whether they should be called true tornadoes. These spinning columns of air often form in tropical areas close to the equator and are less common at high latitudes. Similar natural spinning winds include the gustnado, dust devil, fire whirl, and steam devil.

Tornadoes occur most often in North America, especially in the central and southeastern United States, a region informally called Tornado Alley. The United States has by far the most tornadoes of any country in the world. Tornadoes also occur in South Africa, much of Europe (except most of the Alps), western and eastern Australia, New Zealand, Bangladesh, eastern India, Japan, the Philippines, and southeastern South America, including Uruguay and Argentina.

Scientists and forecasters can detect tornadoes before or as they form. They use pulse-Doppler radar to look for patterns in wind speed and reflectivity data, such as hook echoes or debris balls. Storm spotters also help by watching for tornadoes on the ground.

Rating

See also: Research history of tornadoes

There are several scales for rating how strong a tornado is. The Fujita scale rates tornadoes by the damage they cause, and some countries have replaced it with the updated Enhanced Fujita Scale. The weakest tornadoes, rated F0 or EF0, damage trees but not large buildings. The strongest, rated F5 or EF5, can rip buildings off their foundations and even bend large skyscrapers.

The similar TORRO scale ranges from T0 for very weak tornadoes to T11 for the most powerful known ones. The International Fujita scale is also used to rate the intensity of tornadoes and other wind events based on the damage they cause. To decide how strong a tornado was, experts may also look at radar data, photogrammetry, and ground swirl patterns (called trochoidal marks).

Etymology

The word tornado comes from the Spanish word tronada, which means 'thunderstorm'. That word comes from the Latin tonāre, meaning 'to thunder'. The English spelling moved the r and o around, a change called metathesis. This change was influenced by the Spanish tornado, which means 'to twist, turn'.

A related wind event is the derecho. Unlike a tornado, which covers a small, concentrated area, a derecho is a widespread, straight-line wind. The word comes from the Spanish derecho, meaning 'straight'.

Definitions

A tornado is a violently spinning column of air that touches the ground and hangs from, or sits under, a cumuliform cloud. It is often, but not always, seen as a funnel cloud. To be a tornado, the spinning air must touch both the ground and the cloud base. People do not fully agree on the exact definition. For example, they disagree about whether separate touchdowns of the same funnel are separate tornadoes. The word "tornado" refers to the spinning wind, which is called a vortex, not the cloud around it. Tornadoes are sometimes called cyclones, but in meteorology, a cyclone is a large weather system that spins around a low-pressure center and does not have cloud funnels.

Main article: Funnel cloud

Fast spinning and strong winds lower the air pressure, which can cause water vapor to turn into a visible funnel-shaped cloud because of adiabatic cooling. Some funnel clouds never become tornadoes, and many tornadoes start as funnel clouds without strong winds on the ground. Several tornadoes can form from the same storm cell, and this is called a tornado family.

Characteristics

Most tornadoes look like a narrow funnel, a few hundred meters (yards) across, with a small cloud of debris near the ground. Some are hidden by rain or dust, which makes them especially dangerous, since even experienced meteorologists might not see them. Large tornadoes that look wider than their cloud-to-ground height are called "wedge tornadoes" or "wedges." In the United States, tornadoes are about 500 feet (150 m) across on average, but sizes vary widely. Some are only a few feet wide, while wedges can be a mile (1.6 km) wide or more. A tornado that affected Hallam, Nebraska on May 22, 2004, was up to 2.5 miles (4.0 km) wide at the ground. A tornado in El Reno, Oklahoma on May 31, 2013, was about 2.6 miles (4.2 km) wide, the widest on record. Tornadoes that are dissying can look like ropes, and the winds inside them weaken because of conservation of angular momentum. The average tornado in the United States travels 5 miles (8.0 km) on the ground. The record-holder, the Tri-State Tornado, affected parts of Missouri, Illinois, and Indiana on March 18, 1925, and stayed on the ground for 219 miles (352 km). The 2021 Western Kentucky tornado was on the ground for 165.6 miles (266.5 km).

Tornadoes can be many colors, depending on where they form. Those in dry places may be nearly invisible, while those over water (as waterspouts) can look white or blue. Tornadoes in the Great Plains can look red because of the reddish soil, and those in mountains can look white over snow. Lighting also matters. A tornado that is "back-lit" looks very dark, while one with the sun behind the viewer may look gray or bright white. Dust, rain, hail, and darkness can make tornadoes hard to see, so weather radar or the sound of an approaching tornado may be the only warning. Evidence from Doppler on Wheels mobile radar and eyewitnesses suggests that most tornadoes have a calm center with very low pressure, similar to the eye of tropical cyclones. Tornadoes normally spin cyclonically, which is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Tornadoes are too small for the Coriolis effect to directly control their spin, as shown by their large Rossby numbers. About 1 percent of tornadoes spin in the opposite, anticyclonic direction in the Northern Hemisphere. Their spin comes from complex processes within the storm, including mesocyclones and the rear flank downdraft. Some anticyclonic tornadoes form in rare cases. Tornadoes give off many sounds across the acoustics spectrum, often a whooshing roar that people compare to a freight train or a jet engine. These sounds come from the winds, eddies, and debris. Because many tornadoes can only be heard when very close, sound is not a reliable warning. Tornadoes also produce infrasonic signals that humans cannot hear, and a seismic signal that can be detected in the ground. Tornadoes also give off signals on the electromagnetic spectrum, including sferics and E-field effects. They are linked to patterns of lightning, but tornadic storms do not produce more lightning than other storms. On June 24, 2003, near Manchester, South Dakota, a probe measured a 100-millibar (100 hPa; 3.0 inHg) pressure drop. The pressure fell to 850 mbar (850 hPa; 25 inHg) in the core of a violent tornado. Near a tornado, temperature tends to drop, moisture tends to rise, and atmospheric pressure changes sharply.

Life cycle

See also: Supercell

Tornadoes often develop from thunderstorms called supercells. Supercells contain mesocyclones, areas of spinning air high in the sky, usually 1.6–9.7 km (1–6 miles) across. Most of the strongest tornadoes (EF3 to EF5 on the Enhanced Fujita Scale) form from supercells, which can also bring heavy rain, frequent lightning, strong gusts, and hail. Most tornadoes from supercells begin when rain drags down fast-moving air called the rear flank downdraft. This air pulls the spinning mesocyclone toward the ground. As the mesocyclone lowers, it takes in cool, moist air, and a funnel forms. When the funnel reaches the ground and starts causing damage, it has become a tornado. Scientists still do not fully understand why some storms form tornadoes and others do not.

A tornado is strongest during its "mature stage," which can last from a few minutes to more than an hour. It gets its power from warm, moist air flowing inward from the surrounding area. As the downdraft wraps around the tornado and cuts off this air, the tornado weakens and becomes thin, like a rope. This final stage usually lasts only a few minutes, but the tornado can still cause damage. Winds can even increase during this time because of conservation of angular momentum. Sometimes, in intense supercells, new tornadoes can form in a repeating cycle, with the storm's airflow feeding a new mesocyclone.

Types

Main article: Multiple-vortex tornado

Main article: Waterspout

Main article: Landspout

Main article: Gustnado

Main article: Dust devil

Main article: Fire whirl

Main article: Steam devil

A multiple-vortex tornado has two or more columns of spinning air that turn around their own centers and also spin around a shared middle. Its small areas of heavier damage can appear along the main path. A satellite tornado is a smaller tornado that forms near a large, strong tornado. It may seem to "orbit" the bigger one, but it is a separate spinning column and much smaller. A waterspout is a tornado over water, according to the National Weather Service. Fair weather waterspouts are weaker and more common. They are similar to dust devils and landspouts, and form over tropical and subtropical waters. They most often appear in the Florida Keys and the northern Adriatic Sea. Tornadic waterspouts are stronger, form from severe thunderstorms, and are more dangerous.

A landspout, or dust-tube tornado, is not linked to a mesocyclone. It is sometimes called a "fair weather waterspout on land." Landspouts are usually weaker than classic tornadoes, but they can still cause serious damage. A gustnado is a small, vertical swirl linked to a gust front or downburst. Since it is not connected to a cloud base, scientists debate whether it is a tornado. Gustnadoes can cause small areas of heavier wind damage. A dust devil looks like a tornado, but it forms under clear skies and is no stronger than the weakest tornadoes. Fire whirls form near intense wildfires and are usually not as strong as thunderstorm tornadoes. A steam devil is a rotating updraft that involves steam or smoke. It is very rare and does not have high wind speeds. Hot springs and deserts may be suitable places for one to form.

Intensity and damage

Scales such as the Fujita scale, Enhanced Fujita scale (EF), and International Fujita scale rate tornadoes by the damage they cause. The EF scale updated the older Fujita scale, using expert elicitation, engineered wind estimates, and better damage descriptions. It was designed so that a tornado would get the same number on either scale, and it started being used in the United States in 2007. An EF0 tornado will probably damage trees but not strong buildings. An EF5 tornado can tear buildings off their foundations and even bend large skyscrapers. The TORRO scale goes from T0 for very weak tornadoes to T11 for the strongest known ones. Scientists may also use Doppler weather radar data, photogrammetry, and patterns left on the ground by swirling winds (cycloidal marks) to judge a tornado's strength.

Tornadoes can be strong or weak no matter their shape, size, or location, although strong tornadoes are usually larger. Longer tornadoes tend to be stronger, but this is not always true. In violent tornadoes, only a small part of the path has the strongest winds, mostly from subvortices. In the United States, 80% of tornadoes are EF0 or EF1, and less than 1% are violent. Records may greatly underestimate how many strong and violent tornadoes there are, because damage only shows where a tornado hits buildings or plants. A tornado may be much stronger than its damage shows if its strongest winds happen in an open field. Outside Tornado Alley and North America in general, violent tornadoes are extremely rare, likely because there are fewer tornadoes overall. A few significant tornadoes occur each year in Europe, Asia, southern Africa, and southeastern South America.

Climatology

The United States has more tornadoes than any other country, nearly four times as many as all of Europe, not counting waterspouts. This is mostly because of North America's geography. The continent stretches from the tropics north into arctic areas, and it has no major east–west mountain range to block air flow. In the middle latitudes, where most of the world's tornadoes occur, the Rocky Mountains block moisture and bend the atmospheric flow. The Gulf of Mexico adds plenty of moisture near the ground. Warm and cold air often meet here, which creates strong storms that can last a long time. Many tornadoes form in Tornado Alley in the central United States, an area that also reaches into Canada, especially Ontario and the Prairie Provinces. Southeast Quebec, the interior of British Columbia, and western New Brunswick can also have tornadoes, and so can northeastern Mexico. The United States averages about 1,200 tornadoes a year, and Canada averages 62 reported each year. The Netherlands has the highest number of recorded tornadoes for its size, and the UK comes next. Tornadoes kill an average of 179 people a year in Bangladesh, the highest number in the world. Tornadoes are most common in spring and least common in winter, but they can happen at any time of year. Most tornadoes happen in the late afternoon, and destructive ones can occur at any time of day.

Climate may also affect tornadoes. When the sea surface temperature of a source region, such as the Gulf of Mexico or the Mediterranean Sea, rises, the air holds more moisture, which can lead to more severe weather and tornadoes, especially in the cool season. Some evidence suggests the Southern Oscillation is weakly linked to changes in tornado activity, and research has found fewer tornadoes in the U.S. central and southern plains during El Niño and more during La Niña. Changes in the climate may affect tornadoes through teleconnections that shift the jet stream and larger weather patterns. Although global warming may affect tornado trends, any such effect is not yet clear, because tornadoes are complex and local, and the data has problems.

Detection

Main article: Convective storm detection

Scientists in the United States began trying to warn people about tornadoes in the mid-20th century. Before the 1950s, the only way to detect a tornado was for someone to see it on the ground, so news often reached a local weather office after the storm. Later, weather radar let areas near a local office get advance warning of severe weather. The first public tornado warnings were issued in 1950, and the first tornado watches and convective outlooks came in 1952. In 1953, it was confirmed that hook echoes on radar were linked to tornadoes. By recognizing these patterns, meteorologists could detect storms that probably produced tornadoes from several miles away.

See also: Pulse-Doppler radar and weather radar

Today most developed countries use a network of weather radars to find hook shapes that are likely linked to tornadoes. In the United States and a few other countries, Doppler radar measures how fast winds move toward or away from the radar (direction), so it can spot spinning in storms from over 160 km (100 miles) away. Doppler weather radar can also find mesocyclones inside a supercell thunderstorm, which helps meteorologists predict tornadoes. Radar cannot see everything, though. Distant storms are only seen high up, and tornadoes can form faster than a radar scan. NEXRAD detects signs that suggest tornadoes, not tornadoes themselves, so trained spotters help. In the United States, more than 230,000 trained Skywarn spotters report to the NWS, which can activate sirens and the Emergency Alert System. In Canada, about 1,000 volunteers in Canwarn help spot severe weather, and in Europe, Skywarn Europe and the Tornado and Storm Research Organisation (TORRO) run spotter networks. Spotters look at the back of a supercell for the updraft and a rotating wall cloud, which is a step in tornadogenesis. Only rotating wall clouds spawn tornadoes, and they usually come five to thirty minutes before one. Spotters also watch for a overshooting top, a hard anvil shaped by strong upper level winds, a rear flank downdraft, and the cloud base and surface, since a tornado often forms as the cloud beneath a wall cloud evaporates.

Extremes

The Tri-State Tornado happened on March 18, 1925, and hit parts of Missouri, Illinois, and Indiana. It holds several records. It was likely an F5 on the Fujita Scale, although it happened before scales were used to rate tornadoes. It has the longest path, 352 kilometres (219 miles), and lasted about 3 and a half hours. As of 2026, it is considered the deadliest single tornado in United States history, with 695 deaths. As of 2025, the deadliest tornado in world history was the Daultipur-Salturia Tornado in Bangladesh on April 26, 1989, which killed about 1,300 people. Bangladesh has had at least 24 tornadoes that killed more than 100 people, almost half of the total for the rest of the world.

One of the most widespread tornado outbreaks on record was the 1974 Super Outbreak, which affected a large area of the central United States and far southern Ontario on April 3 and 4, 1974. It produced 148 tornadoes in 18 hours, and more than 300 people were killed. Measuring the wind speeds of the strongest tornadoes is nearly impossible, because ordinary anemometers cannot survive the intense winds and flying debris. Some tornadoes have been scanned by mobile Doppler radar units instead. As of 2025, the fastest wind speed logged this way was from the 1999 Bridge Creek-Moore tornado, with an estimated speed of 486 km/h (302 mph). Debris from a tornado can be carried into the storm that produced it, a process called debris fallout. After a tornado hit Great Bend, Kansas in November 1915, a cancelled check from the town's bank was found in a field outside Palmyra, Nebraska, 305 miles (491 km) away. Waterspouts and tornadoes have been suggested as an explanation for raining fish and other animals.

Safety

Though tornadoes can strike in an instant, there are steps people can take to improve their chances of survival. Authorities such as the Storm Prediction Center in the United States advise having a plan ready in case a tornado warning is issued. When a warning is given, going to a basement or an inside room on the first floor of a sturdy building greatly increases the chances of survival. In areas where tornadoes are common, many buildings have underground storm cellars, which have saved thousands of lives.

Some countries have weather agencies that share tornado forecasts and raise alert levels when a tornado might happen, such as tornado watches and warnings in the United States and Canada. Weather radios sound an alarm when a severe weather advisory is issued for the local area, and they are mainly available only in the United States. Unless the tornado is far away and highly visible, meteorologists advise drivers to park far to the side of the road, so they do not block emergency traffic, and to find a sturdy shelter. If no sturdy shelter is nearby, getting low in a ditch is the next best option. Highway overpasses are one of the worst places to take shelter during a tornado, because the narrow space can have higher wind speeds and debris can be funneled underneath.

Myths and misconceptions

Many people believe a green sky means a tornado is coming, but there is no evidence that a green sky is linked to tornadoes in particular. Many people also think that opening windows will reduce the damage. Air pressure drops a lot inside a strong tornado, but that pressure change is unlikely to cause much damage. Opening windows may make the damage worse, and a strong tornado can destroy a house whether its windows are open or closed. Another common idea is that highway overpasses are safe places to hide. A famous video from the 1991 tornado outbreak near Andover, Kansas shows a news crew and others sheltering under an overpass as a tornado passed nearby. But an overpass is dangerous in a tornado. Those people stayed safe because the storm was weak, it did not hit the overpass directly, and the overpass had an unusual design. Because of the Venturi effect, winds speed up in the narrow space under an overpass. During the 1999 Oklahoma tornado outbreak, three overpasses were hit directly, and at each place someone died. In the same outbreak, more than 2,000 homes were completely destroyed, but only a few dozen people died inside their homes.

An old belief is that the southwest corner of a basement is the safest spot. Actually, the safest place is the side or corner of an underground room facing away from the direction the tornado comes from, which is usually the northeast corner, or the middle room on the lowest floor. Sheltering in a basement, under a staircase, or under a strong piece of furniture such as a workbench gives a better chance of survival. Some people also think that living in a city, or near a big river, hill, or mountain, keeps them safe. Tornadoes have crossed major rivers, climbed mountains, moved through valleys, and damaged several city centers. No area is completely safe from tornadoes, although some areas are more likely to be hit than others.

Ongoing research

Main article: History of tornado research

Meteorology is a fairly young science, and the study of tornadoes is even newer. Tornadoes have been studied for about 140 years and very closely for around 60 years, but some parts of them are still a mystery. Meteorologists understand fairly well how thunderstorms and mesocyclones form and the weather conditions that help them form. However, scientists do not yet fully know how a supercell or other starting processes lead to tornadogenesis, or how to predict which mesocyclones will make tornadoes. Researchers are also studying the low-level mesocyclone and the stretching of low-level vorticity that tightens into a tornado. Intense tornadoes have been seen forming at the same time as a mesocyclone higher up, and some have occurred without a mid-level mesocyclone. The roles of downdrafts, especially the rear-flank downdraft, and of baroclinic boundaries are also areas of intense study.

Predicting how strong a tornado will be and how long it will last is still difficult. Scientists also study tornadoes linked to mesovortices within lines of thunderstorms and within tropical cyclones. Meteorologists still do not know the exact way most tornadoes form, and sometimes tornadoes strike before a tornado warning is issued. To learn more, researchers use in-situ and remote sensing instruments on the ground and in the air, and numerical modeling helps them test ideas in computer simulations. Research programs such as the VORTEX projects (Verification of the Origins of Rotation in Tornadoes Experiment) and TOTO (the TOtable Tornado Observatory) work alongside groups like the National Severe Storms Laboratory, the National Center for Atmospheric Research, and the National Science Foundation, which helps fund much of the work.