Defining A Tornado, How It Is Formed, And Its Main Characteristics

What Is A Tornado Heading

Some readers will never see one, while others experience multiple events in a single year. But most will be very familiar with what a tornado is. We take a closer look at this meteorological phenomenon.

Not only are they famous (or rather infamous) for their dramatic appearance and destructive power, but they have also been made more famous and "glorified" by Hollywood in more than a few of their "disaster movies."

What Is A Tornado?

A tornado is defined as a funnel-shaped, fast-rotating column of air that forms at the base of a storm cloud and extends to the ground. It is characterized by a strong low-pressure center surrounded by rotating high-velocities winds. It typically forms in a supercell with strong up- and downdrafts.

Although they can occur anywhere across the world, the central plains of the United States experience an unusually high concentration of tornadoes every year in a region commonly known as Tornado Alley.

This article examines what exactly a tornado is and how it forms. It also looks at its characteristics and where it typically occurs.  

How A Tornado Is Formed

The majority of tornadoes are formed in violent thunderstorms, especially in what is called supercells. (The most intense and violent form of a thunderstorm.)

The conditions in a supercell need to be ideal in order for a tornado to develop. This means a tornado needs a supercell to develop, but not all supercells can produce tornadoes.

The specific conditions needed for the formation of a tornado is actually a specific combination of wind movements. A combination of both downdrafts (sinking air) and updrafts (rising air) is required for tornado development.

Tornado Formation

The illustration above shows you the complex interaction between cloud formation, wind speeds, and direction, as well as altitude that takes place during the formation of a tornado in a supercell.

Warm moist air near the surface of the ground starts to rise, creating a low-pressure system. As it continues to rise, it is hit by winds with different speeds and blowing in different directions. It is these winds that allow it to start spinning.

This alone is not enough, though. Air rotation near the ground is essential for the process to be completed. As the cold air from the upper atmosphere starts to descend (creating downdrafts), it comes in contact with the updraft, putting pressure on the rising air.

This pressure and friction caused by the downdraft force the space of the rotating updraft to be condensed. This increases the wind speed within the rotating column of air. 

The wind speed is further increased by the rotation towards the axis of the low-pressure system. (Remember, air always flows from an area of high to an area of low pressure)

This acceleration in wind speed towards the axis is called conservation of angular momentum (or spin). This is similar to a figure skater starting to spin on ice. As he/she starts pulling their arms in, they start rotating faster and faster (to conserve angular movement)

The supercell starts acting like a giant vacuum cleaner as the rotating column of air strengthens and sucks more air away from the surface of the ground.

If the combination of "downdraft pressure" and "updraft suction" is strong enough, the column of rotating air will reach the ground, which will complete the formation of the tornado.

As it touches the ground, debris and dirt sucked up by the tornado will form the visible funnel formation we all know so well. (Tornadoes can actually be invisible, but more on that in the next section).

Now that one have a better understanding of how tornadoes are formed, it is easier to understand why certain areas are so prone to the development of tornadoes. 

And this is why the area known as Tornado Alley is such an ideal breeding ground for tornadoes. As the cold, dry air from Canada moves south, it collides with the warm moist air from the Golf Of Mexico over this region.

Here, the Great Plains further contribute to creating this ideal environment, as the relatively flat landscape allows these two air masses to collide and form supercells. The resulting thunderstorms and unstable atmosphere is the perfect recipe for tornadoes to develop.

Characteristics Of A Tornado

Many readers, especially from the Central United States, will already be very familiar with the characteristics of a tornado, especially its almost unmistakable shape.

A tornado is characterized by the very recognizable funnel-shaped fast rotating column of air, with its narrow base touching the ground and then broadening out as it reaches up to the cloud base of typically a cumulonimbus cloud.

Not all tornadoes conform to this familiar image we are so familiar with. There are also a few characteristics of tornadoes that are not that well-known but still very relevant and important to those potentially affected. We take a look at a few of the most important ones:

1) Tornadoes Are Not Always Visible. 

Since a tornado is essentially a fast rotating column of wind, they are not naturally visible by themselves. What makes them visible is the objects on the ground they cross and pick up. 


I already mentioned dust and debris are some of the common objects that are sucked up and give them their familiar grey-brown color. Other objects include vegetation and even water. In the latter case. (As mentioned earlier, when a tornado originates over water, it is referred to as water-sprout.)

A big danger and concern for meteorologists occur as the result of a tornado not being visible, or objects or the terrain masks its visibility. In a heavily wooded region with large trees, for example, it is tough to spot and identify an approaching tornado.

Two other factors that can completely mask a tornado is heavy rain and the cover of darkness. When a tornado occurs during heavy rainfall, the rain-wrapped funnel can be completely invisible until it is too late.

Also, if a tornado occurs at night, you may literally be unaware of it until it is right upon you. Although it makes a loud noise that many people have compared to freight trains or airplanes taking off,  it may be masked if it occurs during a heavy thunderstorm.

These are one of many reasons early warning systems should be in place in areas often affected by tornadoes and why people should always heed these warnings. (Luckily, the accuracy of early warning systems has been greatly improved over the last few decades.)

2) The Unpredicted Path Of A Tornado

People, even experienced observers, still look at an approaching tornado and the path it is following, to make a judgment call to flee/take shelter or stay putt. This is a terrible mistake.

One of the most dangerous aspects of a tornado is the unpredictability of the path it is following. There is a common perception that a tornado follows the path of the storm system it travels in, or that the majority of tornadoes moves from southwest to northeast.

Although there is some truth in these perceptions, tornadoes can veer off-course or completely change direction within the larger storm system without any warning. (Some have even been known to stop and double back on their path.)

Apart from the unpredictable path an established tornado follows, they also have the ability to suddenly appear from literally any direction. Observers have reported tornadoes appearing out of nowhere.

In this case, ideal conditions for the creation of a tornado have been building up, invisible to most observers. Once these conditions have intensified enough, a tornado can literally form and seemingly "appear out of nowhere."  

3) Speed And Size Of A Tornado

Tornadoes literally come in all shapes and sizes. (And don't forget about color, depending on the surface it covers and types of debris it picks up.)

In general, the average tornado is about 200 meters (660 feet) wide, with wind speeds of about 50 miles (80 kilometers) per hour. As far as distance goes, they very seldom travel further than 10 kilometers (6 miles). 

Big Tornado

These are averages, however. Some tornadoes are so small and weak, they are almost unnoticeable. On the other side of the spectrum, some tornadoes are so big and destructive that they have the capability to destroy entire towns.

The most destructive ones can reach wind speeds of up to 300 miles (480 kilometers) per hour and be more than 3 kilometers (2 miles) in diameter.

An example of an extreme tornado that makes your "average tornado" look like a little breeze is the Tri-State tornado of 1925, mentioned earlier in this post. It traveled continuously through parts of Missouri, Illinois, and Indiana for a distance of approximately 362 kilometers (219 miles).

4) Funnel Clouds Creating False Assumptions About Tornadoes

Funnel clouds are a clear indication of the presence of a tornado. Many observers mistakenly use the size of the funnel cloud to try and determine its strength and size.

This is another easy mistake to make, as the funnel cloud is very often not an accurate indicator of size and strength.

In many cases, a hurricane's true size is much larger than the funnel cloud would suggest. In recent history, a tornado near Dodge City in Kansas, was observed with the actual width of the tornado being 3 times larger than the funnel cloud.

Similarly, the size of a tornado is not an indicator of its strength. In fact, a very narrow tornado only a few dozen feet wide can be much stronger and more destructive than one more than a mile wide.

The best way to measure the true impact of a tornado is by using proven standardized scales. The strength of a tornado is normally measured by the Fujita scale. The tornado strength is categorized from EF0 to EF5. 

(With EF0 indicating light damage to vegetation and no structural damage, and EF5 indicating the strongest form of a tornado, which has the ability to rip buildings off their foundation and cause major structural damage to skyscrapers.)

Where Do Tornadoes Occur?

Tornadoes can occur all across the world, especially in the presence of thunderstorms (which create the ideal conditions for the formation of tornadoes).

The highest concentration of tornadoes, however, can be found in North America, especially in Florida and an area called Tornado Alley.

("Tornado Alley" is a broad term coined by the media, and the region can be found in the Great Plains of the Central United States. It is not an official scientific term & meteorologists have not clearly defined the area, but the highest concentration of tornadoes occur here.)

Outside of North America, two of the highest concentrations of tornadoes can be found in Argentina and Bangladesh.


This article provided a clear description of how tornadoes are formed, what makes them work, as well as their most important characteristics. In the process, some misconceptions, dangers, and myths were highlighted. 

It also clearly highlighted the destructive nature and dangers of these meteorological phenomena and focused on their impact on all the areas they encounter.  

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Until next time, keep your eye on the weather!

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