What is a Tornado?
A tornado is a rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction, with wind speeds of up to 300 mph. They can destroy large buildings, uproot trees and hurl vehicles hundreds of yards. Damage paths can be in excess of one mile wide to 50 miles long. In an average year, 1,000 tornadoes are reported nationwide.
How do Tornadoes Form?
Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
When are Tornadoes Most Likely to Happen?
Tornadoes can happen at any time of the year and at any time of the day. In the southern states, peak tornado season is from March through May. Peak times for tornadoes in the northern states are during the summer. A few southern states have a second peak time for tornado outbreaks in the fall. Tornadoes are most likely to occur between 3 and 9 p.m.
Where are Tornadoes Most Likely to Happen?
The geography of the central part of the United States, known as the Great Plains, is suited to bring all of the ingredients together to forms tornadoes. More than 500 tornadoes typically occur in this area every year and is why it is commonly known as "Tornado Alley."
How are Tornadoes Measured?
Though we can look at a tornado and see how big it is, we can't measure its strength that way. Instead, scientists often use the F-scale, or Fujita scale, to measure how strong tornadoes are. The Fujita scale was invented by Dr. Ted Fujita. It would have gone up to F12, but anything above F5 was considered impossible, so that's where the scale ends. Starting Feb. 1, 2007, scientists started using a new, enhanced Fujita scale.
Enhanced Fujita Scale of Tornado Intensity
| Scale | Wind Speed | Possible damage |
| F0 | 65�85 mph | Light damage: Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. |
| F1 | 86�110 mph | Moderate damage: Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken. |
| F2 | 111�135 mph | Considerable damage: Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. |
| F3 | 136�165 mph | Severe damage: Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance. |
| F4 | 166�200 mph | Devastating damage: Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated. |
| F5 | >200 mph | Incredible damage: Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (109 yd); high-rise buildings have significant structural deformation; incredible phenomena will occur. |
What is a Waterspout?
A waterspout is a weak tornado that forms over water. They are most common along the Gulf Coast. Waterspouts can sometimes move inland, becoming tornadoes and causing damage and injuries.
