How are tornadoes formed?

Tornadoes are one of the most violent and dramatic weather types - but how do they form?

When the sun heats the ground, air near the surface is warmed and rises. Typically this air will develop into cumulus clouds at low levels.

But if the atmosphere is unstable, this warm air will continue to rise to far greater heights, and go on to create tall cumulonimbus clouds, the sort you might see during thunder storms.

When this occurs in an environment where wind speeds increase strongly with height, known as wind shear, the higher fast moving air can begin to spin and roll over the slower air below.

This creates an invisible, horizontal wind, spinning and rolling like a cylinder.

As this cylinder develops, powerful warm updraughts tilt it vertically, creating a column of spinning winds.

Thunderstorms that exhibit persistent and deep rotating updrafts such as these are known as 'supercells'.

Falling downdraughts of cold air within the supercell help to bring this column downwards. Eventually the rotation may become so strongly-focused, that a narrow column of violently rotating air forms.

If this reaches the ground a tornado is born.

The most powerful have winds exceeding 400 km/h and can lift trucks and destroy building