Energy. Scientifically speaking, it's the ability to do work (you have just read one of the plainest definitions in scientific thought). Where do tornadoes get all that energy?
Energy comes in many forms. Although energy is neither created nor destroyed, it can change forms. In fact, those transformations help drive the furious winds.
Latent heat of condensation (a form of potential energy) is released when the warm air rises and water vapor condenses into liquid water. This latent heat is the energy that liquid water took in when it evaporated to form the water vapor.
According to Robert Davies-Jones of the National Severe Storms Laboratory, latent heat is the biggest single source of energy in a thunderstorm. The released latent heat warms the rising air parcel, making the storm's air lighter than the air around it.
When the latent heat is released, warms the air. This warming makes the storm's air less dense than the air around it. Since warm air rises, the resulting difference in density pushes the parcel of upward. This creates the extreme speeds needed to create the tornado.
This process shows potential energy changing to kinetic energy. The release of latent heat helps cause differences in pressure, which are another form of potential energy. These pressure differences create wind, transforming the potential energy into kinetic energy as increased wind speed.
The ultimate source of practically all this energy is the sun! The sun's rays shine on the earth, heating up the ground and the water. This heating evaporates water from the oceans, lakes and rivers. The water vapor stores latent heat, the same heat which will later fuels a storm's upward motion.
Tornadoes release lots of energy, says Davies-Jones. A tornado with wind speeds of 200 mph will release kinetic energy at the rate of 1 billion watts -- about equal to the electricity output of a pair of large nuclear reactors.
But the large thunderstorms that spawn tornadoes are immensely more powerful, releasing latent heat at the rate of 40 trillion watts -- 40,000 times as powerful as the twister, Davies-Jones says.
