Tornadoes are extremely violent thunderstorms that develop during certain conditions on the atmosphere. These conditions are met when warm humid air rises to meet colder air. This causes condensation of the moisture and forms a massive thundercloud. This formation is accompanied by strong winds (100 miles per hour) that feed the tornado and carry it to large distances and height. The factors that effect tornado formation include latitude, distance from water body, winds, ocean currents and proximity to mountain ranges.
The strength of a tornado depends upon the extent of instability in the atmosphere and wind shear which refers to the changing wind speed and direction with increasing altitude.
Instability develops when unusually warm moist conditions lower in the atmosphere is contrasted with unusually cold conditions in the upper part of the atmosphere. This place where the two winds meet is called a dry line. While the warm wind continues to rise, it is trapped by the colder air. When the warm air is able to push its way through, and the colder air descends, it causes a spiraling effect. Strong wind conditions cause produce thunderclouds up to 70,000 feet high.
A typical tornado consists of a dark funnel cloud that consists of spiraling moist winds rotating in the anti-clockwise direction. The diameter can range from a few feet of a few kilometers. The probability of having a tornado is high in spring and early summer, compared to other seasons. Also there are areas which are more prone to having tornadoes and known as tornado belts.
Due to the high wind movement, a lot of debris and dust is accumulated by the tornadoes, changing the color of the funnel. Alhough most tornadoes last for only ten minutes or so, the duration can be shorter or even last up to one hour. Tornadoes lose strength and speed with time. The size of funnel decreases gradually and eventually dissipates.
Though tornadoes are known to occur all over the world, its frequency is very high in the United States, east of the Rocky Mountains. Other countries experiencing violent tornadoes are India, Bangladesh, and Argentina. Tornadoes can cause damage depending on their intensity. Most tornadoes are categorized as moderate ones. The ones accompanied with high winds of up to 112 miles per hour can cause intense damage to house, trees and cars. When the speed exceeds 260 miles per hour, tornadoes are capable of lifting and hurling houses and other property across considerable distances.