A tornado is one of the world’s most devastating and violent weather events. Tornadoes can produce the strongest winds on earth, close to 300 miles per hour. Tornadoes may last just a few seconds or move miles across land for hours at a time. Tornadoes can occur almost anywhere in the world though their power and speeds will vary greatly with location. More than one tornado may add power to land falling hurricanes.
Tornadoes are also known as twisters, whirlwinds or waterspouts if over water. They form when a warm wind meets a cold wind and they start to move around each other creating a spinning vortex. A funnel like a corkscrew will come down from the bottom of the storm clouds and can reach the ground. Winds can whirl around up to 300 miles per hour, while pressure at the centre of the vortex is a few hundred millibars lower than outside. This spinning wind is like a giant hoover that sucks up loose objects, trees, animals and even humans. A tornadoes path can be very selective, destroying homes directly in it path, while neighbouring ones are untouched. Although they are usually less than 250 meters wide, their destructive path can cause damage a mile wide for over 50 miles.
The United States of America is famous for the number of tornadoes it has each year, which usually reaches the 1000 mark. Several dozen of these are classed as ‘strong’ or ‘violent’, which means they have reached 200 miles per hour. Although tornadoes can occur anywhere, certain regions are more prone to sightings. In America’s mid-west, near Oklahoma City, an area is known as Tornado Alley because it has more tornadoes than any other place on earth. In 1974, 148 tornadoes were sighted in just 24hours through south and mid-west America. Despite this, it is the United Kingdom that actually experiences the most tornadoes by land area, although most of these are very weak.
Some people are so fascinated by tornadoes that they follow them and watch their development. These ‘Storm Chasers’ have allowed us to learn more about how and where tornadoes form and the damage they can cause. Storm chasing is very dangerous, but some of the best pictures and film of tornadoes has been recorded by chasers.
Knowledge of tornadoes is limited as meteorological apparatus is usually destroyed by the intense winds. Tornadoes are measured by using the Fujita scale that is based on wind speed, but more usually the damage levels.