In order for a vortex – a spiraling funnel of wind – to be classified as a tornado, it must be in contact with the ground and the storm cloud above it

There is simply no natural phenomenon more terrifying than a tornado. Twisters, as they’ve become known, appear almost without warning. They can occur any time during the year, providing the conditions are right.

In order for a vortex – a spiralling funnel of wind – to be classified as a tornado, it must be in contact with both the ground below and the storm cloud above. A tornado’s path is rarely more than 250m across, but can be as much as one mile wide

Tornadoes happen when warm and cool airstreams collide, creating a rotating area of low atmospheric pressure. Air within a low pressure front has a natural tendency to rise and creates a strong upward draught. This draws in surrounding warm air from ground level, causing it to spin faster and faster.

The intensity of a tornado is determined by the Fujita scale:

F1 Tornado - wind speeds between 73-112mph. Even the smallest tornadoes can peel slates from roofs and drive moving cars off the road.

F2 Tornado - wind speeds between 113-157mph. Roofs of some houses will begin to lift off and mobile homes in the tornado’s path would be demolished.

F3 Tornado - wind speeds between 158-207mph. Heavy trees will be uprooted and walls and roofs of solid buildings will be torn away like matchsticks.

F4 Tornado - wind speeds between 208-260mph. Locomotive engines and 40 tonne articulated trucks will be flung around like toys.

F5 Tornado - wind speeds between 261-318mph. Cars are flung like stones for hundreds of metres and entire buildings can be ripped from the ground. The force is similar to that of an atomic bomb.