Tornados In Focus

The pastor of the Lady Lake Church of God, Larry Lynn, picks through the rubble in Lady Lake, Fla., after the church was destroyed by a tornado, early Friday, Feb. 2, 2007. At least 14 people were killed early Friday as thunderstorms and at least one tornado struck central Florida. AP Photo/Orlando Sentinel

Severe thunderstorms tore through central Florida, destroying mobile homes and a church, lifting a tractor-trailer into the air and killing at least 14 people, authorities said. Find out more about what causes tornados.


What Is A Tornado?
Tornadoes are caused by the energy released in thunderstorms. Before thunderstorms develop, changes in wind direction and an increase in wind speed can create a spinning column of air horizontal to the ground.
According to Craig Allen, CBS News meteorologist, these storms are classified as tornadoes only if they touch the ground. Many do not and are called funnel clouds.


How Do Tornadoes Form?
Within the thunderstorm, updrafts of warm, moist air lift the spinning column and tilt it so that it is vertical. If the updraft becomes sufficiently strong, a tornado is formed. Tornadoes that emerge from intense weather systems known as supercells produce particularly powerful twisters when warm air from the ground is lifted into cool, dry air above.

How High Are The Winds?
About 2 percent of tornadoes reach wind speeds of 250 m.p.h. or more.

How Often Do Tornados Occur?
According to the National Oceanic and Atmospheric Administration, in an average year, about 1,000 tornadoes are reported across the United States, resulting in 80 deaths and more than 1,500 injuries.


How Are Tornados Measured?
F-0: 40-72 mph, chimney damage, tree branches broken
F-1: 73-112 mph, mobile homes pushed off foundation or overturned
F-2: 113-157 mph, considerable damage, mobile homes demolished, trees uprooted
F-3: 158-205 mph, roofs and walls torn down, trains overturned, cars thrown
F-4: 207-260 mph, well-constructed walls leveled
F-5: 261-318 mph, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters

Where Do Most Tornados Occur?
Tornados are most common east of the Rocky and west of the Appalachian Mountains during spring and summer. They are associated with strong frontal systems that form on the plains.


To Learn More About Tornados:

• You can read more about tornadoes in a CBSNews.com interactive.

• Click here to obtain official reports of severe weather.

  • Melissa McNamara

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