Tornadoes are violently rotating columns of air that form during severe thunderstorms. They develop when warm, low-pressure air rises rapidly and condenses into a funnel cloud. Tornadoes are classified based on where they form - over land or water. The most powerful tornadoes can have winds over 300 mph and paths of destruction miles long, while smaller "gustnadoes" form from downdrafts. Tornadoes develop within thunderstorms and follow the path of the storm, appearing to "hop" as the vortex is disturbed and reforms along the way. They are rated based on the original Fujita Scale which classified tornado damage and estimated wind speeds.

1. TO RNADOES

2. TornadoesTornadoes are the most powerful, unpredictable and destructive weather systems on Earth. The National Weather Service defines a Tornado as a violently rotating column of air in contact with the earth’s surface (land or water) and commonly associated with a severe thunderstorm.

3. CausesA tornado generally occurs when high winds within a low pressure system (such as a thunderstorm) cause water vapor in the air to condense in to a condensation funnel cloud. Many less severe tornadoes are not even visible to the human eye. Major tornadoes usually become more visible when the strong winds within the funnel lift up dirt and debris off the Earth’s surface. The average tornado has maximum wind speeds of about 112 mph or less, measures around 250 feet in width and travels approximately one mile before falling apart. Some of the most catastrophic tornadoes in recorded history have had winds in excess of 300 miles an hour (twice that of a category 5 hurricane), have measured more than 2 miles in girth, and have carved devastating paths of destruction miles and miles in length.

6. Types of TornadoesTornadoes are generally classified as either aland spout -- a tornado on landwater spout -- a tornado that forms over watergustnado -- a small tornado caused by a strong downburst of wind from a thunderstorm

7. WATER SPOUT

8. LAND SPOUT

9. GUSTONADO

10. How Tornadoes work…Tornadoes don't just pop into existence -- they develop out of thunderstorms, where there's already a steady, upward flow of warm, low-pressure air to get things started. It's kind of like when a rock concert erupts into a riot. Conditions were already volatile; they merely escalated into something even more dangerous.

12. Tornadoes…Some tornadoes consist of a single vortex, but other times multiple suction vortices revolve around a tornado's center. These storms-within-a-storm may be smaller, with a diameter of around 30 feet, but they experience extremely powerful rotation speeds.The tornado reaches down out of a thundercloud as a huge, swirling rope of air. Wind speeds in the range of 200 to 300 mph aren't uncommon. If the vortex touches ground, the speed of the whirling wind (as well as the updraft and the pressure differences) can cause tremendous damage, tearing apart homes and flinging potentially lethal debris.

13. Tornadoes…The tornado follows a path that is controlled by the route of its parent thundercloud, and it will often appear to hop. The hops occur when the vortex is disturbed. You've probably seen that it is easy to disturb a vortex in the tub, but then it will reform. The same thing can happen to a tornado's vortex, causing it to collapse and reform along its path.Smaller tornadoes may only thrive for a matter of minutes, covering less than a mile of ground. Larger storms, however, can remain on the ground for hours, covering more than 90 miles and inflicting near continuous damage along the way.

14. Tornado Ratings…Tornadoes are among the most dangerous storms on Earth and, as meteorologists strive to protect vulnerable populations through early warning, it helps to classify storms by severity and potential damage.Tornadoes were originally rated on the Fujita Scale, named for its inventor, University of Chicago meteorologist T. Theodore Fujita. The meteorologist created the scale in 1971 based on the wind speed and type of da­mage caused by a tornado. There were six levels on the original scale.