what causes tornadoes
Tornadoes are caused by an imbalance in the atmosphere containing kinetic energy. Updrafts in clouds occur when heat is released from air vapor condensing in the air.
Tornadoes are caused by wind sheer. This occurs when the wind rapidly changes direction, causing a circular motion in the atmosphere.
Colliding air masses typically are the causes of tornadoes. For further information, you can visit: http://www.mnn.com/earth-matters/translating-uncle-sam/stories/what-causes-tornadoes.