Tornadoes are formed when hot air and cold air meet in a powerful storm, and the warm air begins spiralling upward, creating a funnel cloud. This funnel cloud forces objects on the ground and in the air around and upward, and can be strong enough to uproot trees, move cars and tear apart buildings. This extremely energetic air current is part of a special, very tall storm called a supercell.
The supercells that make tornadoes form when a large mass of cold air moves over a large mass of warm air. This situation is highly unstable, because the warm air is lighter than the cold air. The greater the temperature difference, the more unstable the situation. Winds are generated as the warm air moves up and through the cold air and the cold air moves down and around the warm air. If the warm air contains a large amount of water vapor, it tends to condense into clouds as it moves up and cools.
When this movement of warm air upward is energetic enough, the moving air starts to twist on its way up, creating the potential for a funnel cloud. These funnel clouds are the effect of rapidly moving and spinning warm air and condensing water vapor going upward and spiraling.