Atmosphere And Weather

Tornado how Tornadoes Form



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No one can predict with accuracy where a tornado will touch down. When conditions are right weather forecasters can offer warnings for different areas, but the strength of the tornado is often unknown until it takes place. With windspeeds reaching up to 300 miles an hour, tornadoes weave a path of death and destruction when they touch down. There are three main kinds of tornadoes:

- Weak tornadoes account for 60% of all that occur and usually have a low death toll. They can last from one minute to just over ten minutes and have a windspeed of about 100 miles an hour.

- Average tornadoes can last from 20 to 25 minutes or longer and account for about 60% of the tornadoes. Windspeed in this type of tornado can range from 110 205 miles an hour.

- Violent tornadoes are very devastating to the location and the people affected accounting for 70% of tornado deaths. Along with the extreme windspeeds, such a tornado can last an hour or longer.

No matter what type of tornado occurs, certain atmospheric conditions must be present in order for it to form. They develop in warm moist air that is moving ahead of a cold front in an eastward direction. The first indication of the possibility of a tornado is a thunderstorm and a tornado can develop in the early stages. It is almost always transparent until it starts to pick up dust and debris from the ground in its funnel shape.

There are five main developments that take place in the atmosphere in the formation of a tornado. According to weather forecasters, the main element is that the air mass has to be unstable with the potential for a thunderstorm.

1. When the conditions are right for a thunderstorm to develop, the change in the direction and speed of the wind creates a horizontal spinning effect in the lower levels of the atmosphere.

2. As the warm, moist air is pushed upward by the approaching cold front, this causes an updraft that changes the horizontal spin of the wind into a vertical one.

3. This vertical shift brings about an area of rotation within the thunderstorm that can be from 2 to 6 miles wide. The strength of the rotation will determine the strength of the tornado that results.

4. The lower cloud base of a tornado is free of rain.

5. A tornado forms from the rotation and travels in a straight line picking up everything in its path.

Tornadoes can occur at any time of the year and in any region where the weather conditions are right. That being said, there are periods of the year when they are more likely than others, such as between March and May in the southern states of the US. The amount of devastation that results depends on the population of an area. A tornado could touch down in a sparsely populated area and not do any damage at all because there are no people or houses affected.

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