Tornadoes stretch from cumulonimbus clouds as funnels of spinning air, touching the ground. Sometimes they hurt people and damage houses. They are found in different parts of the world, but mostly in the United States. Most are not very large, but the winds in a tornado can be stronger than the winds in a hurricane. They don't last very long, and most tornadoes don't hurt people, but some of them can lift cars and buses and even destroy buildings. Meteorologists usually know when tornadoes might happen, so that you can get warning to get to a tornado shelter or other safe place.
A tornado is a vortex of air that blows things around and picks things up. Tornadoes come from powerful thunderstorms called severe thunderstorms. Only a few thunderstorms grow strong enough to make tornadoes. Most tornadoes happen in the spring and summer when the air is warm and humid, but they can happen in fall or winter. In the summer, you might see dust spinning in a field. Meteorologists call these dust whirls or dust devils. Dust devils help us a little to understand tornadoes.
There's a lot we don't know about tornadoes because they are too dangerous to get close to and measure, and because most of them have very short lives. We are not exactly sure how all tornadoes form but for many, it seems to start with wind shear. That’s when wind changes speed or direction at different altitudes. If a stronger wind is just above a lighter wind, wind shear can make air roll along the ground, like a tube. If this tube of rolling air is near a growing thunderstorm, the rising air of the thunderstorm can lift it and stand it up while the tube of air keeps spinning. The thunderstorm grows and stretches the tube to make it taller and faster. The cumulonimbus cloud may then develop a portion of clouds that starts to spin fast in the air. This is a funnel cloud. If the funnel cloud moves down to the ground, it is a tornado. Other names for a tornado are twister, cyclone, whirlwind, or vortex.
In the United States every year, over 1,000 tornadoes touch down. They usually are smaller than a football field. Most tornadoes last less than 10 minutes and don't cause a lot of damage or hurt people. Most tornadoes happen in the warm part of the day, in the afternoon or evening. That's when thunderstorms can grow very large. Twisters do happen at night.
Tornadoes can be different colors. When they start off as funnel clouds, they are whitish or gray. Once they touch down over a field, they pick up soil and become brown. At night they are very hard to see, and even in the day you might not see one that is hidden by clouds, rain, trees, or buildings.
Tornadoes can move in any direction, typically around 30mph. That's about as fast as a car moving down a quiet street. If the thunderstorm is moving fast, then the tornado can move at over 50mph. There are some tornadoes that can be a mile wide, and last for an hour. These monster twisters can have winds over 200 mph. Big tornadoes are violent and make loud roaring sounds like a train or an airplane. When they get this powerful, they can wipe almost anything out of their way. That's why you need to know tornado safety rules.
A mobile home sitting on blocks is a bad place to be in during a tornado. Even if the home is tied to the ground, a strong wind can knock it over and tear it apart. A wind that might only damage the roof of a regular house might cause a disaster for a mobile home.
In the United States, one of the best things you can have to warn you of tornadoes is a Weather Radio. In most places, whenever there is dangerous weather that might cause an emergency, you will hear it on the weather radio. Good weather radios have alarms for dangerous weather, and they run on batteries too, in case you lose electricity. Most cell phones automatically receive tornado warnings too.
On days when there might be severe thunderstorms or tornadoes, meteorologists at the National Weather Service alert you with a weather watch. A Tornado Watch means watch the sky and be alert because tornadoes might happen. This is when you, and your family or school must make plans so that you don't get caught in a dangerous spot by mistake. If a Tornado Warning is posted, that means a tornado is very likely or already happening. Take shelter.
After a tornado passes, we measure how much damage it made and then compare it to the Enhanced Fujita Scale. The Enhanced Fujita Scale or EF-Scale is named after a famous Japanese tornado research scientist, Dr. Ted Fujita. The weakest tornadoes are EF-0 and the strongest are EF-5.
When tornadoes happen over water, there's little damage to measure. Tornadoes over water are called waterspouts. Waterspouts that form on mostly sunny days, without thunderstorms, are weak, but they can turn over small boats, and they can move onto land where they fade quickly. Waterspouts that form from strong cumulonimbus clouds are more dangerous as they are more likely to remain as tornadoes after moving on land. You should treat waterspouts the same way you treat regular tornadoes.
When stormy weather is possible, listen to the forecast on TV and radio. Always have a plan for dangerous conditions. It always helps if someone in your school, job, or home knows First Aid in case somebody gets injured.