Tornadoes

Tornadoes

Introduction What can lift roofs from buildings, sweep houses into the air, and rip trees out by the roots? Tornadoes can! Tornadoes come in many sizes. Some tornadoes are narrow-only a few feet (1 meter) across. Others are more than a mile (1. 6 km) wide. The biggest tornado on record was almost 2. 6 miles wide (4. 2 km). It struck Oklahoma in 2013. Some tornadoes touch down for a short period of time. Others can travel for hundreds of miles, destroying everything in their paths while carrying houses and cars over long distances.

How Tornadoes Form What causes tornadoes? Scientists aren't sure. They know that the strongest and most violent tornadoes come from large thunderstorms called supercells. These thunderstorms form when warm, moist air rises into the atmosphere and mixes with cold, dry air higher in the sky.

Scientists think that in some supercells, the warm air rises quickly and the cold air rushes in to replace it. This causes the air to rotate. The spinning air begins to form clouds into a funnel shape. The funnel cloud stretches downward with winds up to 300 miles (483 km) per hour. When the funnel touches the ground, it officially becomes a tornado.

Some scientists think that tornadoes occur to balance the temperature and moisture levels in the air.

Measuring Tornadoes While scientists are still researching the causes of tornadoes, they have a system for estimating their strength. A scientist named T. Theodore Fujita developed the Enhanced Fujita scale, known as the EF Scale, as a way to rate a tornado's strength based on wind speed. Because it's difficult to get close to a tornado, scientists estimate its wind speed by examining the damage it causes. The most powerful tornadoes are rated EF-5. They have winds greater than 200 miles (322 km) per hour.