The three main causes (or ingredients) for a tornado are:

  1. Colliding air masses – Warm, humid air near the ground meeting cold, dry air above, which creates strong thunderstorms and an unstable atmosphere.
  1. Strong wind shear – Winds changing speed and direction with height, which makes the air start to spin horizontally and sets up the rotation needed for a tornado.
  1. Powerful thunderstorm updrafts (often in supercells) – A strong rising column of air that tilts the horizontal spin into a vertical, rotating updraft (a mesocyclone), from which a funnel cloud can form and reach the ground as a tornado.