Tornadoes are the mixture of warm,moist air and cold,dry air. When they combined the warm air is rising and the cold air is sinking, also known as convection.Convection is able to mix the cold and warm air. The warm air gets caught on the cold wind shear and so the convection starts to form a tornado.
Tornadoes, What Are They
Tornadoes start from a super cell thunderstorm(a thunderstorm that last longer than a regular storm). It is also tornado is a violent rotating piece of air that then goes to a stationary front (warm and cold winds combining).The rotation is formed by winds at different altitudes then creating a wind shear(rate of the wind speed changes).