How do Tornadoes Form

Tornadoes are considered to be the most destructive form of natural thunderstorms. The devastation they leave behind is massive. Sights of destroyed homes, fallen trees, and vehicles overturned and thrown away, are very common after a tornado. A few of these violent tornadoes even notch up speeds close to 500 kph.

Causes of Tornado Formation

There are no exact reason as to why one is formed. There are many different theories doing rounds about the formation of tornadoes. The most popular of these is the one which believes that they occur due to the collision of large volumes of air, having different temperatures. Collision mostly occurs in places where warm and cold air are present together. For a tornado to form, warm air has to be present at the bottom, while the cool air at the top. When warm air tries to rise up, a large updraft is formed, which can lead to a tornado, if the biometric air pressure under the updraft is very low.

Tornadoes are formed only under certain types of climatic conditions and that's the reason why they occur frequently in some parts of United States and not the rest. During spring, the climatic condition between the Rocky and Appalachian Mountains is very conducive for their formation. This is due the fact that moist, warm air from the Gulf of Mexico, collides with the dense, cool air of the mountainous regions. The states around this region are the most likely to face a tornado and therefore are called 'tornado alley'. The various states included in the 'tornado alley' are - Missouri, Indiana, Colorado, Texas, Nebraska, Kansas, Oklahoma, Illinois and Arkansas.

Method of Tornado Formation

1. Prior to the development of actual thunderstorms, it is observed that there is a change in the direction of the wind. Along with the change in direction, the speed of wind increases and it starts rising upwards. This leads to an invisible, horizontal spinning effect in the lower atmosphere, which later changes to a vertical position.
2. Once the thunderstorm starts moving vertically, its circumference also keeps on increasing. Strong wind starts rotating within the circumference, which could be anywhere between 2 to 6 miles wide.
3. A lower cloud base is formed in the area of the wind rotation, which is called a rotating wall cloud and it later expands to become a tornado. Along with tornadoes, hailstorms and strong winds blowing in one direction are also observed.

Not all that form are the same, and vary in terms of their impact and destruction they cause.

Factor	Weak Tornadoes	Strong Tornadoes	Violent Tornadoes
Wind speed	Less than 110 mph	Between 110 to 205 mph	More than 205 mph
Lifetime	1 to 10 minutes	20 minutes or more	60 minutes or more
Tornado deaths reported	Less than 5%	Around 30%	Around 70%
Share in total tornadoes	69%	29%	2%

It is evident from the table that the violent tornadoes are rare, and are the most destructive. Almost 69% of the tornadoes are weak and are not very destructive in nature and less than 5% are life-threatening. Given below is an account of some of the major tornadoes to have occurred in the United States over the years:

Year	Place	Deaths Reported
1974	Ontario to Alabama	315
1965	Mid-west region of USA	271
1925	Indiana, Missouri and Illinois	695
1903	Georgia	203

After reading about the causes for the formation of tornadoes, there are chances that people might believe that these storms occur only in certain areas of the United States. It is true that tornadoes are more frequent in the above mentioned places, but tornadoes can strike anywhere and anytime, if the climatic conditions are conducive. In the United States alone, on an average, around 800 tornadoes are reported resulting in around 1500 deaths every year. Meteorologists rely on weather radars which provides them with necessary information about strong winds and developing storms, after which they issue warnings to the people. Keep an eye on these warnings, and in case of one, try following certain safety tips.