How tornadoes are formed

While no two tornadoes are the same, there are certain conditions that are required for their formation. A tornado's development can be described by a sequence of distinct phases.

How are tornadoes formed?

There are two important aspects needed in the formation of a tornado, geography and rotation. The formation and life cycle of tornadoes can be explained in a series of stages:

Tornado formation - Stage One Tornado formation - Stage One  

Stage One

Sunshine heats the ground causing convection and an upward movement of air referred to as a thermal. As the ground temperature increases, moist air rises and meets cold, dry air above it.

The warm air rises forming low level shallow cumulus clouds which become trapped under the layer of warm, dry air and eventually form into the heavier and denser cumulonimbus clouds (also known as a thunder cloud).

At this stage is the dust- whirl stage which results in light debris being twisted and lifted from the ground, the development of a funnel cloud also occurs here.

Tornado formation - Stage Two Tornado formation - Stage Two  

Stage Two

This stage can be referred to as the organizing stage where the funnel cloud descends and becomes stronger.

As the strong wind currents move through the cloud from opposite directions, they cause rapid changes in speed and direction, referred to as wind shear. As the winds travel higher, they begin to rotate and as the spiral tightens, the winds become increasingly violent.

Thunderstorms commonly form in late afternoon and contribute to the rotation and formation of a supercell. A supercell is characterised by a large scale rotation of a strong updraft.

Tornado formation - Stage Three Tornado formation - Stage Three  

Stage Three

The updraft eventually spirals down to reach land and narrows resulting in a faster rotation. The rotating updraft reaches towards the ground as a funnel cloud but only becomes classified as a tornado when it reaches ground.

This is the mature stage and can be when the most damage occurs during the tornado due to the funnel cloud being at its widest and of a near- vertical angle.

At the end of the life cycle of a tornado, the tornado begins to shrink and the funnel becomes tilted and eventually diminishes, conditions are still dangerous throughout this stage. The tornado then enters the decay stage in which it weakens in width resulting in an eventual break up.

Last updated: 26 July 2013