Tornadoes

A tornado is a violently rotating column of air that is in contact with the surface of the earth and a thunderstorm in the atmosphere.

Tornadoes occur where warm, humid air collides with cold, dry air. Wind speeds can reach up to 300 miles an hour and range between 70m and 3 km across. Tornadoes can last from a few minutes to an hour.

Where do they occur?

Tornados can occur on any continent but the vast majority occur in the Tornado Alley region of the United States. On average the USA has about 1,200 tornadoes a year with most occurring in the spring and least occurring in the winter.

Causes of tornadoes

• Intense or unseasonable heat causes the air above the ground to heat up and start to rise.
• The warm moist air then meets the cold, dry air above and rises up through it causing an updraft.
• This updraft will begin to rotate if winds vary sharply in speed or direction.
• A visible funnel forms and descends from the cloud.
• When the funnel touches the ground it becomes a tornado.

How are they measured?

The most commonly used measure of a tornado is the Fujita scale which rates tornadoes by the amount of damage they cause, from F0 to F5.