What is a Tornado?

A tornado is a rapidly rotating column of air extending from a thunderstorm to the surface of the Earth.

This mobile, funnel-shaped cloud typically advances beneath a large storm system. Tornadoes are visible because, nearly all the time they ave a condensation funnel made up of water droplets, dust, dirt, and debris.

While a tornado may go by many names like “whirlwind,” “windstorm,” “cyclone,” “twister,” and “typhoon,” they are important to understand because they are the most violent atmospheric storm.

Keep reading to become a tornado expert and learning everything from quick tornado facts to how to track these destructive and even deadly storms.

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What Causes a Tornado? / How do Tornadoes Form?

A lot of people wonder: “How do tornadoes form?” These severe weather events typically stem from thunderstorms, although they don’t have to.

Wind shear is one of the most critical components for the formation of a tornado. Wind shear is the change of direction and speed of the wind with height. This can create a horizontal spinning effect within a storm cell. The rotating air of an updraft meets the rotating air of a downdraft and creates that iconic and scary funnel cloud you’re probably used to seeing.

Typically, this combination of winds can happen when moist, warm air meets cool, dry air. When these air masses meet, they create instability in the atmosphere, which allows wind to change direction, move faster, get higher, and start that rotation we mentioned above.

Where do Tornadoes Occur?

A map of the U.S. showing the Significant Tornado Alley
Source: Cancannon et al, 2000 https://www.nssl.noaa.gov/users/brooks/public_html/concannon/

Now that you know how tornadoes form, it’s easier to understand why tornadoes occur where they do.

Tornadoes occur in many places across the globe, but they are most likely to form in the United States. In fact, the United States has more tornadoes each year than any other country.

The area of the country with the highest concentration of tornadoes is in an area dubbed “Tornado Alley.” This is also the area where there are the most frequent strong tornadoes.

Tornado Alley is a nickname for the Great Plains where tornadoes often occur. This is the graphic our Chief Meteorologist, Mark Hoekzema, refers to when explaining Tornado Alley.

This is the area in the Central United States between the Rockies and the Appalachian Mountains. Some states often associated with Tornado Alley include South Dakota, Nebraska, Kansas, Oklahoma, Texas, and Colorado. If you want to get specific, Oklahoma and Texas see the most tornadoes per year per 10,000 miles.

Tornadoes are so frequent in this region because the moist, warm air from the Gulf of Mexico frequently meets the cool, dry air from Canada, which prompts formation.

Florida also sees its fair share of tornadoes thanks to its frequent thunderstorms.

Outside of the United States, tornadoes also occur in high concentrations in Bangladesh and Argentina.

It’s important to note that powerful, deadly tornadoes can and have occurred in other places that are not on this list. It’s important to always be prepared for severe weather regardless of your location.

When Are Tornadoes Most Likely?

A tornado forming oview a field

Since there are specific meteorological conditions necessary for tornado formation there are times when tornadoes are more likely to form. In the United States, there are tornado seasons for various regions. Peak tornado season for the Southern Plains is from May to early June, while it’s earlier in the spring for the Gulf coast region, and later for the northern plains and upper Midwest (June to July).

When it comes to the time of day, tornadoes can happen at any time. They are most likely to occur somewhere between 4 and 9 p.m. It’s important to note that tornadoes can and have occurred in times other than included above. Some of the most deadly tornadoes have occurred at night as people are indoors and sleeping. It’s important to always be prepared at any time of day and adhere to any tornado watches or warnings in the area.

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How is Tornado Strength Rated?

Enhanced Fujita Scale showing the classification of hurricanes and wind speeds for each one

Like hurricanes, tornadoes have different strength classifications based on wind speeds. The only problem is that it’s nearly impossible to measure the actual wind speed inside a tornado. Most weather stations don’t make it through one of these storms unscathed!

Instead we make an estimate based on the damage left behind.

In order to make a close estimate, Dr. Ted Fujita developed a scale back in 1971. After some adjustments in the early 1990s from Dr. Fujita himself and a consensus from a panel of meteorologists and engineers in the early 2000s, we now used what is called the Enhanced Fujita (EF) Scale. We’ve been using this scale to rate tornadoes since 2007.

A lot of these injuries and deaths occur because people don’t have enough time to seek appropriate shelter. That’s why knowing the warning signs for when a tornado may occur is so important (along with early warning systems and accurate forecasting).

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What Are the Warning Signs a Tornado May Occur?

There are a few tell-tale signs a tornado may develop. The most common warning is a funnel shaped cloud. If you see a rotating cloud in the shape of a funnel slowly making its way towards the earth, it can become a tornado. Even if you’re far away you’ll be able to tell this a rotating cloud rather than just a moving one. Another obvious warning sign is falling debris.

Next you should watch out for an incredibly dark sky or a dark sky with a greenish tint. The green coloring comes from sunlight reflecting off hail stones, which typically accompany tornadoes and the storms that precede them.

In some cases, there can be an eerie calm after a strong thunderstorm has occurred before a tornado hits. This is because tornadoes form on the rear right quadrant of strong thunderstorms and away from the heaviest rain and hail. You should not go out immediately after a strong storm has ended; especially if you have been under a tornado warning. It’s best to stay put for 15-30 minutes.

That’s not all. You can also tell a tornado is on the way if you hear loud, persistent roar. This continuous rumble will sound a lot like a freight train and is a sign that a tornado could occur or already has occurred and is closing in.

Earth Networks Total Lightning Network total lightning data for a 20-mile radius around Beauregard, Alabama on March 3, 2019 when the deadly tornado outbreak happened

There is another warning sign a tornado may occur that you might not be able to tell on your own. That sign is a high frequency of in-cloud lightning. This can be tricky to spot on your own because in-cloud lightning never touches the ground. Warning systems that utilize total lightning detection can detect these high frequencies and give people more time to prepare for possible tornadoes.

Tornado Watches and Warnings

Another way to protect yourself from tornadoes is by paying attention to tornado watches and warnings. The National Weather Service (NWS) shares tornado watches and tornado warnings to help people stay updated on the chances of severe weather.

What’s the difference between a tornado watch and a tornado warning?

A Tornado Watch

In the case of a tornado watch:

  • Tornadoes are possible
  • Remain alert for approaching storms
  • Watch the sky and stay tuned to a NOAA Weather Radio, commercial weather radio, or television for further information


Tornado Warning

In the case of a tornado warning:

  • A tornado has been sighted or indicated by weather radar
  • Take shelter immediately


Tornado Prediction

How do you predict a tornado? Predicting exactly when and where a tornado will form and move is not possible with current technology.

A waterspout, or tornado that forms over a body of water

However, meteorologists can predict tornadoes by looking for conditions that are favorable for tornado development. They mail do this by using the output from very powerful computer forecast models.

Massive computer programs called numerical weather prediction models help meteorologists decide if conditions will be right for the development of a tornado. They work by calculating what the atmosphere will do at certain points over a large area, from the Earth’s surface to the top of the atmosphere.

These models gather data from weather balloons twice per day in addition to data from satellites, aircraft, and surface weather stations. The models start with these current weather observations and attempts to predict future weather, including supercells, using physics and dynamics to mathematically describe the atmosphere’s behavior.

There is also the aspect of ensemble forecasting, which is used to account for all the times weather “breaks the rules.” Instead of using just one model, ensemble forecasting relies on a supercomputer to run several models at a time. If each run looks similar, then meteorologists can assume the weather will likely follow the rules. However, if the runs look different in different places then meteorologists understand something in the atmosphere is causing the weather to misbehave.

There is also the aspect of total lightning detection. Since high frequencies of in-cloud lightning can be a warning sign a tornado has formed or could form, meteorologists and everyday users who rely on total lightning detection systems can keep an eye on in-cloud lightning frequencies to help predict.

Tornado Detection

But how are tornadoes detected?

That’s a good question that doesn’t come down to as much of a science as tornado prediction.

A lot of tornado detecting is based on what forecasters and storm spotters or storm chasers (Like our meteorologist, Mark Ellinwood) can see with their bare eyes. There are certain thunderstorm features like green sky or a funnel-shaped cloud that help people predict them. There are more advanced visual cues as well like a rear-flanked downdraft. Storm spotters are trained to recognize tornadic conditions and report what they see to the National Weather Service.

The other way we detect tornadoes is with radar imagery. Patterns in radar, like the tornadic vortex signature (TVS), are a good indication that a tornado has developed. Computer programs, called algorithms, analyze Doppler radar data and display it in ways that make it easier for forecasters to identify tornadoes.

A hook echo, which is a tell tale sign a tornado has formed on radar

A hook echo from our friends at NOAA and NSSL


When a Doppler radar detects a large, rotating updraft that occurs inside a supercell, it is called a mesocyclone. Mesocyclones are typically 2-6 miles in diameter. This is much larger than the tornado that may develop within in.

Another pattern important for tornado detection is a hook echo. This is a pattern in radar reflectivity images that looks like a hook extending from the radar echo, usually in the right-rear part of the storm. The hook is often associated with a mesocyclone and indicated favorable conditions for tornado formation.

Another way we currently detect tornadoes is with dual-polarization radar technology which allows organizations like the National Weather Service to see debris. This gives meteorologists a high-degree of confidence a damaging tornado is on the ground. It’s especially helpful at night when tornadoes are difficult to see with the human eye.

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What to Expect Before, During, and After a Tornado

If you’re wondering what you should do before a tornado you can start by planning your tornado safety plan for key locations like your home and business. When you have solid plan for any type of severe weather event you are more likely to survive.

Can you survive being caught in a tornado? Yes, of course. But only if you know what to do before, during, and after.

Before a Tornado 

The United States government advises citizens to do the following before a tornado in order to remain safe:

1. Know your area’s tornado risk

In the U.S., the Midwest and Southeast have a greater risk for tornadoes.

2. Know the signs of a tornado

These include a rotating, funnel-shaped cloud; an approaching cloud of debris; or a loud roar.

3. Sign up for your community’s warning system.

The Emergency Alert System (EAS) and National Oceanic and Atmospheric Administration (NOAA) Weather Radio also provide emergency alerts. If your community has sirens, then become familiar with the warning tone. Earth Networks Dangerous Thunderstorm Alerts (DTAs) also provide tornado warnings with substantial lead times.

4. Pay attention to weather reports.

Meteorologists can predict when conditions might be right for a tornado.

5. Identify and practice going to a safe shelter

Your first choice is a safe room built using FEMA criteria or a storm shelter built to ICC 500 standards. The next best protection is a small, interior, windowless room on the lowest level of a sturdy building

A lot of people wonder: “Is it safe to be in a bathtub during a tornado?”

Interior bathrooms and bathtubs are a good place to hide during a tornado, but you should avoid all exterior rooms, including bathrooms.

Remember: It is NOT safe to be in a car during a tornado as tornadoes can lift and even throw cars. You should also avoid overpasses and bridges. You are safer in a low, flat location.

6. Make A Tornado Safety Kit

We also recommend having a tornado safety kit at your home and workplace. These safety kits should include emergency items like:

A red check mark with a transparent background Battery-powered radio

A red check mark with a transparent background Flashlights

A red check mark with a transparent background Extra batteries

A red check mark with a transparent background Prescription medications

A red check mark with a transparent background First-aid kits

A red check mark with a transparent background Water and canned/dried food

During a Tornado

Now that you know what to do before a tornado it’s time to learn what you can expect during a tornado. Tornadoes are very scary and personal experiences can differ from the below tips from the U.S. government, but this is a good starting point, so you at least know what to expect.

A red check mark with a transparent background Immediately go to a safe location that you identified.

A red check mark with a transparent background Take additional cover by shielding your head and neck from flying debris with your arms and putting materials such as furniture and blankets around you.

A red check mark with a transparent background Listen to EAS, NOAA Weather Radar, local alerting systems, or commercial alerting systems for current emergency information and instructions.

Car driving away from a very large tornado funnel cloud

DO NOT try to outrun a tornado in a vehicle on or foot. This is especially important for businesses to understand when planning their emergency response plan to keep employees safe and secure.

A common response of employees when it comes to severe weather is to try and go home, or even stop and pick up the kids from school. This is even greater if employees have families or pets there. It’s imperative that employees understand the importance of staying put during tornadoes and other forms of dangerous weather.

Remember that one of the worst places you can be during a tornado is in a vehicle and DO NOT leave the safety of a building to get into your car.

If you are stuck in a car or outdoors and cannot get to a building or tornado shelter, heed Tip #2 and cover your head and neck with your arms and cover your body with a coat or blanket, if possible.

After a Tornado

Now you know the steps to take before and during a tornado, you’re probably wondering what you should do after a tornado hits.

Damaged home as a result of a tornado

First thing’s first: Make sure the threat is really gone.

Keep listening to EAS, NOAA Weather Radio, and local authorities for updated information until they give you the all clear to venture outside. Sometimes there can be multiple tornadoes in the area at once. When the same weather system spawns multiple tornadoes this is called a tornado outbreak. Tornado outbreaks typically consist of six to ten tornadoes that typically occur on the same day and in the same region. Make sure it’s completely safe outside and all tornado watches and warnings are lifted before you leave your shelter.

What you should do next depends on your situation.

If you are trapped:

  • Cover your mouth with a cloth or mask to avoid breathing dust.
  • Try to send a text, bang on a pipe or wall, or use a whistle instead of shouting for help.


If you are unharmed:

  • Stay clear of fallen power lines or broken utility lines.
  • DO NOT enter damaged buildings until you are told they are safe by first responders.
  • Save your phone calls for emergencies. Phone systems are often down or busy after a disaster. Use text messaging or social media to communicate with family, friends, and coworkers.
  • Be careful during clean-up. Wear thick-soled shoes, long pants, and working gloves.
  • Photograph any damage to your home or business before you start cleaning up for insurance purposes.
  • If your home is without power, use flashlights or battery-powered lanterns rather than candles to prevent accidental fires.


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Fast Tornado Facts

There are plenty of tornado facts and myths out there. Our meteorologists have listed five of the most common and dangerous tornado myths along with the correct information to help you understand this severe weather phenomenon and stay safe from it.

Tornado Myth #1: Opening windows equalizes pressure

Do not open windows during a tornado watch or warning. This will not equalize pressure and limit damage to your home. Instead, you and everything in your home will be in greater danger as debris can fly in or you could be next to the window when it blows out. Keep windows secure and most importantly: Stay away from windows and doors!

Tornado Myth #2: Tornadoes only form on flat land

While tornadoes are most common in the Great Plains that doesn’t mean they only form on flat land! Rivers, mountains, valleys, and tall buildings do not stop tornadoes from forming. Tornadoes impact large cities and can even form on water (these are known as waterspouts).

Tornado Myth #3: All tornadoes are visible as they approach

We’ve mentioned this already, but tornadoes can be invisible. Wind is invisible so unless a tornado has picked up debris and has condensation, they can be hard to see. Heavy rain can also cloak tornadoes until they are too close for you to seek shelter. Trust your ears, not your eyes. Remember a loud roar (like a freight train) is a good sign a tornado is approaching.

Tornado Myth #4: If a tornado is not coming towards me, I’m safe

Tornadoes do not follow a specific pattern or route. Therefore, they can unexpectedly change speed and direction at any time and come right at you. There’s no safe place to observe or film a tornado from. The only safe place is in a location that offers shelter from high winds and debris.

Tornado Myth #5:  It’s safer to abandon my vehicle for the shelter of an overpass

This is an extremely dangerous tornado myth. While vehicles are one of the most dangerous places to be during a tornado, underneath an overpass may be the only place that’s worse. While a highway overpass is a sturdy structure that may offer protection from flying debris, it will not protect you from dangerous winds. In fact, it can act as a wind tunnel and may cause accelerated wind that collect debris, causing you more harm. If you are in your vehicle during a tornado you should pull it over to the side of the road, get out, and lay flat in a nearby ditch while covering your neck and head.

Here ‘s a short video with some more tornado facts your may find useful.

Big, Bad, Famous Tornadoes

There are plenty of famous tornadoes that have impacted the U.S. and the world, but what is the biggest tornado ever recorded?

Tornado moving towards a town

Central Oklahoma holds the record for both the largest and the strongest tornadoes ever recorded. The largest tornado recorded to date touched down in El Reno, Oklahoma on May 31, 2013. It measured 2.6 miles wide at one point.

The strongest tornado ever recorded to date occurred in 1999 just south of Oklahoma City. This insane F-5 tornado plowed through Oklahoma with recorded winds of over 300 mph. A tornado of this size recorded today would even max out the Enhanced Fujita Scale established in 2007.

Besides being the largest or strongest, tornadoes are often remembered for being the deadliest. A lot of the deadliest tornadoes occurred at times in our history where tornadoes were impossible or difficult to predict and when warnings were difficult to share but this isn’t always the case.

Here are the top five deadliest tornadoes ever recorded in the world.

1. Dhaka, Bangladesh in 1989

The deadliest tornado on record occurred on April 26, 1989 in the Dhaka region of Bangladesh. This massive storm killed at least 1,300 people and injured over 12,000. Additionally, 80,000 people were left homeless after this destructive storm.

2. Tri-State Tornado in 1925

The deadliest tornado in U.S. history is the “Tri-State Tornado.” This tornado killed 695 people and injured 2,027 over a 300-mile span through Missouri, Illinois, and Indiana. It was rated F5 at the top of the old Fujita scale and occurred on March 18, 1925.

3. Natchez Tornado in 1840

The third tornado was the “Natchez Tornado” which killed 317 people and injured 109 back on May 6, 1840. This tornado hit hardest along the Mississippi River in Louisiana and Mississippi and the Federal Emergency Management Agency says it’s important to note that the total death toll may not have included slaves.

4. Louis Tornado in 1896

The fourth deadliest tornado in the U.S. was the “St. Louis Tornado” which killed 255 people and injured 1,000 on May 27, 1896 in Missouri and Illinois. It had winds of between 207-260 mph.

5. Tupelo Tornado in 1936

The fourth deadliest tornado was the “Tupelo Tornado.” Ravaging the northeast Mississippi City on April 5, 1936, the “Tupelo Tornado” killed 216 people and injured 700 more.

More recently, a tornado struck Joplin, Missouri on May 22, 2011, killing 158 people and injuring more than 1,000 others. It became one of the deadliest tornadoes in U.S. history despite that fact that the National Weather Service considered it a “warned” event in which advance notice of the tornado was given, critical information was communicated and received, and most people sought the best shelter available to them.

So what happened? A NOAA assessment of this event found that some residents had become desensitized to tornado sirens and warnings, and that “initial siren activation has lost a degree of credibility for many residents.” This is combination with a high population density in the path of the storm, contributed to the high death toll.

Tornado News and Videos

While most of the tornadoes on the list of big, bad famous tornadoes were probably before your time, tornadoes are still a common occurrence today. Over the past few years, we’ve covered powerful tornadoes across the globe in places like Brazil, Greece, Uruguay, Belarus, and Canada.

Nashville Tornadoes

In the early morning hours of March 3, 2020, destructive tornadoes ripped through Nashville. These storms decimated homes in Wilson, Putnam, Davidson, and Benton counties and claimed the lives of 24 people.

Earth Networks cell tracks, DTAs, and NWS storm reports from Nashville Tornado on March 3, 2020

2011 Super Outbreak

In 2011 there was a super outbreak in the eastern half of the United States. Between April 25 and 28, 258 confirmed tornadoes touched down. Four of those were classified EF-5 on the Fujita Scale.

According to NOAA’s Storm Prediction Center, at least 358 people died during this tornado outbreak with 238 of those deaths occurring in Alabama. This remains the most prolific tornado outbreak on record. Tuscaloosa and Birmingham became nearly unrecognizable. See the before and after from NOAA and the National Centers for Environmental Information.

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2017 NFL Tornado

A tornado scare made headlines a few years ago during the 2017 NFL playoffs.

Storms rolled over AT&T Stadium as the Dallas Cowboys hosted the Green Bay Packers on January 15. Fans and team members were unable to leave the stadium for three hours after the end of the game due to a tornado warning from the National Weather Service prompting a “shelter-in-place” protocol from the stadium. While there were no reported tornadoes in the area, the staff made the right call as over 72,000 total lightning strikes bombarded the north Texas area during and after the game.

2019 Alabama Outbreak

A tornado outbreak in March 2019 also made headlines. A tornado outbreak is the occurrence of multiple tornadoes from the same synoptic scale weather system. The number of tornadoes to require qualifying an outbreak typically range from six to ten. On May 3rd, 2019, 41 tornadoes touched down in just 6 hours.

The strongest tornado in this outbreak, an EF4 that touched down near Beauregard, Alabama, took the lives of 23 people. You can read more about this Alabama tornado outbreak and our analysis of it on our blog.

Earth Networks Total Lightning Network cell tracks, Dangerous Thunderstorm Alerts, and National Weather Service (NWS) alerts during the March 3, 2019 Alabama tornado outbreak

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Tornado Quiz


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