How do Tornadoes Form?

Tornadoes are notoriously difficult to predict accurately as scientists still do not fully understand exactly how they are formed. Generally speaking, if cold, dry air comes into contact with warm, moist air, there is the potential for tornadoes to develop. This happens on a cold front and several tornadoes may develop on a particularly active front.

• Severe thunderstorms known as 'supercell thunderstorms' can form near to the front. These have extremely powerful updraughts that can reach up to the top of the cloud. There is a large change of wind direction and an increase in wind speed with increasing height near the front. This 'vertical wind shear' causes the updraught to rotate, causing a spinning motion in the lower atmosphere.
• Rapidly-rising air (convection) within the storm cloud moves this spinning motion (rotation) towards the vertical.
• This rapid rotation extends downwards towards the surface, initially as a funnel cloud. If conditions are favourable, it will reach the surface (touch down) as a tornado.