According to infoplease, tornadoes can cause very minimal damage, such as ripping siding off of homes, to catastrophic damage, which can literally lift homes off their foundations. The type and severity of tornadoes are classified using the Fujita scale. On this scale, tornadoes are rated from F0 to F5, with F5 being the most dangerous and deadly.
Depending on the type of tornado involved, the types of damage incurred can vary dramatically. For example, F2 and F3 tornadoes can have wind speeds of up to 112 mph, which is strong enough to overturn cars and mobile homes, as well as tear the roofs off of houses and twist and uproot trees. Tornadoes designated as F0 and F1 do very little damage, but may result in broken tree limbs and damaged signs. They may even blow off a few shingles.
The most deadly tornadoes, on the other hand, only account for 1 percent of funnel clouds. These storms are rated F4 and higher. These storms have funnels that measure in excess of a mile wide and carry winds in excess of 261 mph. These storms completely level communities and hurl objects considerable distances. They also account for more than 70 percent of tornado fatalities.