From the Field

Tornado facts: How they form and how to prepare

Tornadoes pack furious winds and often leave death and destruction in their path. Here are some basic tornado facts and tips on how to prepare.

Tornadoes can happen anywhere, packing furious winds and often leaving death and destruction in their path. But being aware and prepared can help ensure your family’s safety.

Here are the tornado facts you need to know to better understand how they work, what to do if you’re in a tornado’s path, and how you can help people affected by disasters in the United States.

What is a tornado?

A tornado is a violently rotating column of air extending from the base of a thunderstorm down to the ground. A tornado is not always visible unless it forms a funnel made up of water droplets, dust, and debris. The average tornado travels 3.5 miles and can last from 10 seconds to more than an hour. The wind speeds of tornadoes are not officially measured, but the most powerful tornadoes are estimated to have gusts stronger than 200 mph.

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What is a tornado watch?

If an area is under a tornado watch, that means a tornado is possible and you should be prepared. You can prepare by reviewing and discussing your family emergency plans, checking supplies and your safe room, and being aware of any new weather alerts for your area. Weather forecasters typically issue a tornado watch for a broad area, like an entire county.

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What is a tornado warning?

If an area is under a tornado warning, that means a tornado is expected and you should act now and seek shelter. This means people have seen a tornado or radar has detected one in the area, and it poses a risk to life and property. If you don’t have a cellar or underground basement, move to an interior room on the lowest floor of a sturdy building. Weather forecasters typically issue a tornado warning for a small area, like a city. Many cities across the U.S. have sirens that alert residents to a tornado warning.

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What causes a tornado?

A tornado forms when the wind within a storm system changes speed and direction. This creates a spinning effect, which is tipped vertically by an updraft through the thunderclouds. The deadliest tornadoes are produced by supercell thunderstorms — storms with a rotating updraft called a mesocyclone that forms an anvil-shaped cloud. Supercells can also bring damaging hail, severe winds, lighting, and floods. Certain theories suggest that tornadoes are caused by temperature changes, but some of the most destructive tornadoes began with minimal temperature changes.

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What is the Tornado Alley?

The southern plains of the central United States consistently experience a high frequency of tornadoes, earning the nickname, Tornado Alley. Here, tornadoes typically form in late spring and occasionally the early fall. The Tornado Alley runs from northern Texas through Oklahoma, Kansas, Nebraska, and South Dakota. These plains are more likely to form supercell thunderstorms, which often produce destructive tornadoes.

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What makes a tornado so destructive?

The intense high winds of a tornado — also called a twister — are powerful enough to knock over trees, flatten buildings, and destroy roads. But one of the major destructive forces of a tornado is the debris that turns into projectiles. Traveling through a populated area, the funnel of a tornado picks up and carries millions of small and large items, including trees, rocks, trucks, parts of houses, and broken glass. These missiles cause damage proportionate to their size and speed when blown into buildings or homes or when falling back to earth.

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What is the rating scale for tornadoes?

Since 2007, tornadoes are now rated on the Enhanced Fujita scale, with ratings from EF0 to EF5. It is nearly impossible to accurately measure the speed of a tornado, as any measurement device would be destroyed. The EF scale is determined based on an estimated 3-second gust of wind, which is calculated according to the degree of damage on 28 different damage indicators — from softwood trees to schools. For example, for a tornado to completely destroy a large shopping mall or a large section of the structure, the wind speed would be estimated at 204 miles per hour, with a range from 176 to 247, which would classify it as an EF5.

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What is an EF5?

An EF5 is the most powerful tornado, causing incredible damage with winds over 200 miles per hour. It is capable of destroying schools, large shopping malls, and causing permanent structural deformation to a 20-story building. It is rare, accounting for only 1% of all tornadoes — yet causing 37% of tornado-related fatalities. The National Weather Service maintains a list of all the EF5 tornadoes since 1950.

The two most recent EF5 tornadoes hit Moore and El Reno, Oklahoma, in 2013 and 2011, respectively. Each caused widespread loss of life and property damage.

The largest tornado ever recorded also hit El Reno on May 31, 2013, only 11 days after the historic twister in Moore. The 40-minute-long tornado was rated an EF3 but measured 2.6 miles across at its peak growth.

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How do I prepare for a tornado?

The Federal Emergency Management Agency provides guidelines to help you and your family prepare for and stay safe during and after a tornado. Its guide will help you and your community reduce risk when a twister does hit your area.

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How can I help people affected by disasters in the U.S.?

  • Pray for children and families impacted by disasters.
  • Give to provide life-saving aid and relief supplies to survivors of U.S. disasters like the devastating Moore tornado.
  • Volunteer to help World Vision respond to disasters or assist communities in the U.S. with disaster preparedness.

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Chris Huber and Andrea Peer of World Vision’s staff in the U.S. contributed to this article.

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