The Fujita Tornado Damage Scale, or F-Scale, is a rating scale that measures the wind speed of a tornado. A level ranging from F0 to F5 (from weakest to strongest) is assigned based on how much damage the tornado has been observed to cause. The scale also included levels F6 to F12, but these are theoretical. The F-Scale was introduced in 1971 by Dr. T. Theodore Fujita; in 2007 the F-Scale was replaced by the EF-Scale, or Enhanced Fujita Scale, which readjusted the winds speeds because the old scale did not take variations in building quality into account. An unrated label of "EF no rating" covers the F6 to F12 speeds. Weather Underground notes that these speeds would result in "inconceivable damage."
Even strong structures may not be able to withstand tornadoes, and some tornadoes have been seen to rip asphalt from the ground. The stronger the wind speed, the more likely the sight of heavily damaged buildings and grounds. An F0 tornado will not cause much structural damage; you may see damaged tree branches or roofs, and windows broken by flying objects. Anything that might be lifted or moved by regular winds may be affected.
As wind speed increases, stronger tornadoes can actually lift houses from their foundations, as happened in the Jarrell, Texas, tornado of 1997. In a May 28, 1997 interview with Elizabeth Farnsworth of PBS, Austin American-Statesman reporter Jerry White noted that houses had been "just taken off the slabs."
The initial damage from tornadoes is from the high winds; however, people and animals can be killed when hit with flying debris, or crushed by the debris when dropped by the tornado. People and animals also are picked up, thrown about and possibly killed upon landing by the strong winds.
Damage is not limited to just the immediate effects on structures or people and animals. The National Severe Storms Laboratory says there is also an economic cost comprised of rebuilding costs; temporary shelter and emergency services costs; revenue loss from destroyed businesses; lost income from people being either injured or killed; and crop damage.
Waterspouts are essentially tornadoes over water, although not all waterspouts form under tornadic conditions. Some tornadoes that begin over water, known as "fair weather" waterspouts, form when the surface of the water is warm and humidity levels are high. Waterspouts may begin as land tornadoes and move out over water, or begin over water and move onto land. Over water they won't do much damage unless they encounter some sort of water craft or over-water structure, but if a strong enough waterspout moves inland, it can create damage similar to that of a tornado that formed over land. A waterspout off the coast of Carlsbad, California, in 1992 moved inland and damaged several trailers at a mobile home park.
