A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a large rain cloud.
Most tornadoes have wind speeds less than 110 miles per hour, are about 76 metres across, and travel several kilometers before losing all its energy and dissipating. However, some extreme tornadoes can attain wind speeds of more than 300 miles per hour, stretch more than two miles across, and stay on the ground for more than 100 km!
These violent weather events can rip paths of destruction through towns and cities and kill large numbers of people.
Although, no two tornadoes are the same, they all need certain conditions before they can form – particularly intense heat.
- As the ground temperature increases, warm, wet air heats up and starts to rise.
- When this warm, moist, air meets cold dry air, it explodes upwards, puncturing the air layer above. At this stage a thunder cloud may begin to build.
- This develops into a storm – there may be rain, thunder and lightning.
- Winds from different directions can case the upward moving air to rotate
- This forms the characteristic cone shape we associate with tornadoes.
Tornado Strength Scale
There are several scales for rating the strength of tornadoes. The Enhanced Fujita Scale (EFS) rates tornadoes by the amount of damage caused by the tornado. This is the most common rating scale used by most countries.
The Enhanced Fujita Scale splits tornado strength into six categories.
Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes occur in the Tornado Alley region of the United States.