Although tornadoes occur in many parts of the world, these destructive forces of nature are found most frequently in the United States east of the Rocky Mountains during the spring and summer months. In an average year, 800 tornadoes are reported nationwide, resulting in 80 deaths and over 1,500 injuries.

A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. Damage paths can be in excess of one mile wide and 50 miles long.

Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height create an invisible, horizontal spinning effect in the lower atmosphere.

Rising air within the thunderstorm 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.

Weak Tornadoes: 69% of all tornadoes, less than 5% of tornado deaths, lifetime 1 - 10+ minutes, winds less than 110 mph.

Strong Tornadoes: 29% of all tornadoes, nearly 30% of all tornado deaths, may last 20 minutes or longer, winds 110 - 205 mph.

Violent Tornadoes: Only 2% of all tornadoes, 65% of all tornado deaths, lifetime can exceed 1 hour, winds greater than 205 mph.

WHAT TO LISTEN FOR

Tornado Watch: Tornadoes are possible in your area. Remain alert for approaching storms.

Tornado Warning: A tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your predesignated place of safety.

Remember: Tornadoes occasionally develop in areas in which a severe thunderstorm watch or warning is in effect. Remain alert to signs of an approaching tornado and seek shelter if threatening conditions exist.

Look out for: dark often greenish sky, large hail, wall cloud, loud roar similar to a freight train, circular rotation in the clouds.

CAUTION: Some tornadoes appear as a visible funnel extending only partially to the ground. Look for signs of debris below the visible funnel. Some tornadoes are clearly visible while others are obscured by rain or nearby low-hanging clouds.

WHAT CAN YOU DO?

Before the Storm:

(1) Develop a plan for you and your family for home, work, school and when outdoors

(2) Have frequent drills

(3) Know the county in which you live (and its shape so you can identify it on TV weather alerts) and keep a highway map nearby to follow storm movement from weather bulletins

If a Warning is Issued or If Threatening Weather Approaches:

(1) In a home or building, move to predesigned shelter, such as a basement

(2) If an underground shelter is not available, move to an interior room or hallway on the lowest floor and get under a sturdy piece of furniture

(3) Stay away from windows

(4) Get out of automobiles

(5) Do not try to outrun a tornado in your car; instead, leave the area immediately

(6) If caught outside or in a vehicle, lie flat in a nearby ditch or depression

(7) Mobile homes, even if tied down, offer little protection from tornadoes and should be abandoned

(8) Take an AM/FM or NOAA Weather Radio (tuned to 162.4500 mhz ) with you

Occasionally, tornadoes develop so rapidly that advance warning is not possible. Remain alert for signs of an approaching tornado. Flying debris from tornadoes causes most deaths and injuries.

See also tips under Thunderstorms. Thunderstorms always accompany tornadoes.