The cause of a tornado

When warm southern winds try to rise, the cold northern air blocks them. They hit each other, causing the warm trapped air to rotate horizontally between the two. The sun warms the earth below, and more warm air continues to rise. It finally pushes it's way through the colder air. The cold air then begins to sink and it sends the warm air spinning upward. The warm air spins faster and faster and eventually a funnel cloud forms and touches the ground. It's not quite a tornado until it makes landfall.