Every time before a thunderstorm forms, the wind changes direction and their is an increase in wind speed with increasing height forms an invisible rotating effect in the bottom part of the atmosphere.

The rising air within the thunderstorm makes the rising air vertical instead of horizontal.

Image here and above not by us.

In the thunderstorm there is a spot that is 4-12km wide, this is where most of the larger tornadoes are formed.

Image made by us.