How do tornadoes form?

Steps

Diagram/Picture

Explanation/Write-up

1

 

Tornado formation starts as a horizontal, spinning tube of air.

 

Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.

 

2

 

The tube is pulled vertically into an updraft.

 

Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.

 

3

 

The mature storm continues to rotate and may produce a tornado

 

An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

 

4

 

Picture of a wall cloud, copyright Ron Przybylinski.

A lower cloud base in the centre of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free. Note rain in the background.

5

 

Picture of a tornado copyright Ron Przybylinski

Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm.

Tornadoes usually result from a very large thunderstorm. Cold air and warm air combine, and the cold air goes down as the warm air rises. This warm air eventually twists into a spiral, forming a funnel cloud. As the sky turns a very dark green colour, the tornado begins its path of destruction.

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