What causes a tornado? All you need to know

In this article, Interesting Engineering (IE) explores what tornadoes are and the factors contributing to their formation. We discuss the meteorological conditions that must be present for a tornado to occur. 

We also cover the various types of tornadoes and what happens when one strikes. What's the greatest danger from tornadoes to human life? IE reveals this too.  

What is a tornado?

A tornado is a powerful and destructive weather phenomenon that occurs when strong winds and thunderstorms collide. It is a violently swirling column of air extending from a thunderstorm to the ground. Since tornadoes are basically air, they can be hard to spot until they create a condensation funnel of water droplets, dust, and debris.

The average forward speed of a tornado is about 10 to 20 miles per hour. But these swirling columns of air can be nearly stationary or reach wind speeds of over 300 miles per hour.

Tornadoes can occur anywhere in the world. Still, a region in the central United States called the 'Great Plains' has the highest frequency and intensity of tornadoes of any place on earth. This area is known as 'Tornado Alley,' and it includes Texas, Oklahoma, South Dakota, Louisiana, Kansas, Nebraska, and Iowa. Roughly 1,200 tornadoes hit the U.S. yearly.

The National Weather Service introduced a scale known as the "Enhanced Fujita Scale" in 2007 to "score" tornadoes based on the damage a tornado caused. Tornado-related damage is used to help estimate the range of wind speeds the tornado likely produced. From that, a rating (from EF0 to EF5) is assigned.

What are the main causes of a tornado?

The collision of warm, moist air and cold, dry air causes tornadoes. When these two air masses meet, they create an area of low pressure, as the warm air rises through the colder air, which can cause the air to start spinning. As the rotating updraft draws in more warm air from the thunderstorm, its rotation speed increases. This spinning air turns into a tornado when it comes into contact with the ground. 

Several meteorological conditions must be present for a tornado to form. Some of the most common causes of a tornado include the following:

• Moist, warm air

Tornadoes need a source of warm, moist air to feed on. For the Tornado Alley in the U.S., this air typically comes from the Gulf of Mexico or the Pacific Ocean.

• Cold, dry air

Tornadoes also need a source of cold, dry air to help fuel the storm. This air typically comes from Canada for tornadoes occurring in the United States. 

• A strong jet stream

A jet stream is a fast-moving current of air that flows high in the atmosphere. When the jet stream is strong and moves in the right direction, it can push the warm, moist air and cold, dry air together, creating the conditions needed for a tornado to form.

• A front

A front is a boundary between two different air masses. When a cold front moves into an area with warm, moist air, it can create the conditions needed for a tornado to form.

• An unstable atmosphere

An unstable atmosphere is one in which the air is prone to rising and falling quickly. When the atmosphere is unstable, it is more likely that a tornado will form.

• Wind shear

Wind shear is a change in wind direction or speed over a short distance. When wind shear is present, it can cause the air to spin, eventually turning into a tornado.

What are the types of tornadoes?

There are several different types of tornadoes, each with its own characteristics and level of intensity. Two primary types of tornadoes, with their subtypes, are explained below.

Supercell tornadoes

A supercell is any thunderstorm with a mesocyclone (an updraft that rotates around a vertical axis) occupying its core. The most common type of tornado comes from a supercell thunderstorm. They can be the most potent and destructive tornado type and are characterized by strong rotating updrafts.

A supercell tornado is usually larger and more intense than a non-supercell tornado. Supercells can also produce various severe weather phenomena, including large hail, strong winds, and of course tornadoes.

Supercell tornadoes have the following subtypes:

• Multi-vortex tornado

A multi-vortex tornado is a type of tornado with multiple vortexes, or small areas of low pressure, spinning within the larger tornado. These types of tornadoes tend to be more destructive than single-vortex tornadoes.

The widest tornado ever recorded was a multiple-vortex tornado. This struck El Reno, Oklahoma, on May 31, 2013, and is notable for claiming the lives of four tornado chasers- the first known deaths in storm-chasing history. The storm's maximum recorded windspeed was at least 302 miles per hour (486 kilometers per hour), and its largest width was 2.6 miles (4.2 km). The 2013 El Reno tornado caused $35–40 million worth of damage, killed 20 people, and was classified as an EF3 tornado.

• Wedge Tornado

A wedge tornado is characterized by a large, broad, relatively low-hanging funnel cloud that appears wedged into the ground. Wedge tornadoes are typically larger and more intense than other types of tornadoes. They can cause significant damage to structures and vegetation.

• 'Tornadic' waterspouts

'Tornadic waterspouts,' often known as 'tornadoes over water,' can be created by supercell thunderstorms in a manner that is the same as land-based tornadoes- except they just happen over water. Tornadic waterspouts would also include a tornado that crosses from land to water.

Non-supercell tornadoes

Although the largest and deadliest tornadoes occur in supercell thunderstorms, many tornadoes also occur in non-supercell clouds and storms. Tornadoes that do not originate from structured storm-scale spinning are referred to as non-supercell tornadoes.

• Gustnado

The gustnado is a type of non-supercell tornado.  It develops along a storm's gust front and is characterized by a whirl of dust or debris at or near the ground with no condensation funnel.

• Waterspout

The term "non-tornadic" or "fair-weather waterspouts" refers to the vast majority of waterspouts, which are not connected to a supercell thunderstorm's revolving updraft. Fair-weather waterspouts occur in coastal waters. They are usually weaker than their land-based counterparts and are typically short-lived.

• Landspout

A landspout is a tornado with a small, rope-like condensation funnel similar to that of waterspouts that develops while the thunderstorm cloud is still forming. There is no rotating updraft in a landspout; instead, the spinning motion comes from a location close to the ground.

What happens during a tornado?

During a tornado, strong winds and thunderstorms collide, creating a swirling column of air that touches the ground. These winds can reach speeds of up to 300 miles per hour and can cause significant damage to buildings, homes, and infrastructure. 

Tornadoes can last for a few minutes or several hours, and their size and intensity can vary greatly. Some tornadoes are small and weak, while others are large and destructive. A tornado sometimes causes other dangerous weather conditions, such as hail and lightning, which can worsen the damage.

What are the effects of a tornado?

All tornadoes create damage of some kind. Still, the most severe ones have the potential to uproot homes, launch cars into the air, and transform broken glass and other debris into deadly projectiles. The greatest danger from tornadoes to people is wind-borne flying debris.

These powerful storms can cause significant damage to buildings, homes, and infrastructure and disrupt essential services such as electricity and water.

In addition to physical damage, tornadoes can also have serious emotional and financial impacts on those affected. The loss of a home or personal belongings can be traumatic, and rebuilding and recovering from a tornado can be financially burdensome. 

 With all this in mind, the effects of a tornado can be devastating, to say the least.

Tornado Facts

Below, you can find some interesting tornado facts:

• Tornadoes most commonly occur in the United States, particularly in the Midwest and Southeast.
• The United States sees an average of 1,200 tornadoes per year.
• Tornadoes can reach wind speeds of more than 300 miles per hour.
• The Fujita scale, or F-scale, measures the intensity of a tornado based on the damage it causes. The scale ranges from F0 (minor) to F5 (incredible).
• The average width of a tornado is about 300 feet, but some can be as wide as 2.5 miles.
• Tornadoes can occur at any time of day, but they are most common in the afternoon and evening.

Tornadoes: Concluding notes

Tornadoes are powerful swirling storms of violent air and can cause severe damage. Depending on their proximity to populated areas and structures, this destructive weather phenomenon has the potential to cause significant damage and disruption to communities.

While scientists know the specific meteorological conditions needed for tornadoes to form, they are still researching exactly what triggers a tornado.

It is crucial to have an emergency preparedness plan in case a tornado strikes your area and to seek shelter immediately if a warning has been issued.