Learn English with EnglishClass101! Don't forget to stop by EnglishClass101.com for more great English Language Learning Resources! -------Lesson Dialog------- ----Formal English---- TORNADOES TWISTER! A house is destroyed in seconds. A car is thrown into the air. A train is flipped upside down. A tree is ripped out of the ground by its roots. These things are the result of twisters, or tornadoes— nature’s most violent weather. WHAT IS A TORNADO? A tornado is a very strong column of air that is spinning. It stretches from a thunderstorm down to the ground. Some tornadoes spin faster than others. The fastest winds spin up to 300 miles per hour. On the ground, most tornadoes are less than one-quarter of a mile wide. However, some can be wider than a mile. Most tornadoes are on the ground between ten and thirty minutes. The strongest tornadoes can be on the ground for more than an hour. HOW TORNADOES FORM Most tornadoes form from very large thunderstorms called supercells. These storms form when warm, moist air is trapped under cool, dry air. As the warm air rises, it gets cooler and forms clouds and thunderstorms. Sometimes the air begins to spin very fast around a funnel or tube shape. If the spinning wind touches the ground, it becomes a tornado. Scientists aren’t sure why some supercells produce tornadoes and others don’t. WHERE TORNADOES FORM Tornadoes can form almost anywhere. However, the United States has more tornadoes than any other country. Every year, the United States has about one thousand tornadoes. Canada is second with about one hundred tornadoes every year. Most tornadoes form in an area called Tornado Alley. This flat area is in the middle of the United States. Warm, moist air from the Gulf of Mexico meets cool, dry air from Canada. Tornado Alley also gets warm, dry air from the Southwest. WHEN TORNADOES FORM Tornadoes can form at any time of the year. Most tornadoes form between early spring and the middle of summer. May and June have the most tornadoes. More than seven hundred tornadoes formed in April 2011. That was the most tornadoes in a single month since records have been kept. On April 27, 2011, 207 tornadoes formed in a 24-hour period. That’s the most tornadoes in a single day. MEASURING TORNADOES Weather scientists do not have an exact way to measure a tornado’s winds. Instead, they use the Enhanced Fujita Scale to measure the damage. Wind speeds are estimated. RECORD-BREAKING TORNADOES The Deadliest in the World In 1989, a huge tornado struck the Asian country of Bangladesh. It killed at least 1,300 people and hurt 12,000 others. About 80,000 people were left homeless. The Deadliest in the United States The 1925 Tri-State Tornado traveled 219 miles and was on the ground for four hours. It started in Missouri, crossed southern Illinois, and entered Indiana. It also holds the U.S. record for the most deaths (695) caused by a single tornado. It also holds the record for the longest tornado track. The Most Expensive A huge tornado struck Joplin, Missouri, in 2011. Over one hundred people died, and over a thousand were hurt. About eight thousand buildings were destroyed. The cost to fix the damage was almost three billion dollars. STUDYING TORNADOES Most people want to stay far from tornadoes. But storm chasers get close to tornadoes to study them. Storm chasers use special instruments to get information about tornadoes. They hope to learn how to help people and homes stay safer when a tornado strikes. WEATHER REPORTS Tornadoes form fast, and most of them last less than an hour. As a result, weather scientists can’t always warn people a long time before a tornado strikes. They let people know when a thunderstorm is likely to produce a torna [...]