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. Once a tornado in Broken Bow, Oklahoma, carried a motel sign 30 miles and dropped it in Arkansas!
Reference : http://news.bbc.co.uk/2/hi/science/nature/7533941.stm
What causes tornadoes?
Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. These thunderstorms often produce large hail, strong winds, and tornadoes. Tornadoes in the winter and early spring are often associated with strong, frontal systems that form in the Central States and move east. Occasionally, large outbreaks of tornadoes occur with this type of weather pattern. Several states may be affected by numerous severe thunderstorms and tornadoes.
During the spring in the Central Plains, thunderstorms frequently develop along a "dryline," which separates very warm, moist air to the east from hot, dry air to the west. Tornado-producing thunderstorms may form as the dryline moves east during the afternoon hours.
Along the front range of the Rocky Mountains, in the Texas panhandle, and in the southern High Plains, thunderstorms frequently form as air near the ground flows "upslope" toward higher terrain. If other favorable conditions exist, these thunderstorms can produce tornadoes.
Tornadoes occasionally accompany tropical storms and hurricanes that move over land. Tornadoes are most common to the right and ahead of the path of the storm center as it comes onshore.
Frequency of Tornadoes
Tornadoes can occur at any time of the year.
1. In the southern states, peak tornado occurrence is in March through May, while peak months in the northern states are during the summer.
2. Note, in some states, a secondary tornado maximum occurs in the fall.
3. Tornadoes are most likely to occur between 3 and 9 p.m. but have been known to occur at all hours of the day or night.
4. The average tornado moves from southwest to northeast, but tornadoes have been known to move in any direction. The average forward speed is 30 mph but may vary from nearly stationary to 70 mph.
5. The total number of tornadoes is probably higher than indicated in the western states. Sparce population reduces the number reported.
Tornado Safety
What YOU Can 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/parish in which you live, and keep a highway map nearby to follow storm movement from weather bulletins.
4. Have a NOAA Weather Radio with a warning alarm tone and battery back-up to receive warnings.
5. Listen to radio and television for information.
6. If planning a trip outdoors, listen to the latest forecasts and take necessary action if threatening weather is possible.
If a Warning is issued or if threatening weather approaches:
1. In a home or building, move to a pre-designated 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 it immediately.
6. Mobile homes, even if tied down, offer little protection from tornadoes and should be abandoned.
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