What Causes Tornadoes

How Tornadoes Form

Tornadoes form under a certain set of weather conditions in which three very different types of air come together in a certain way.

Near the ground lies a layer of warm and humid air, along with strong south winds. Colder and strong west or southwest winds lie in the upper atmosphere.

Temperature and moisture differences between the surface and the upper levels create what we call instability, a necessary ingredient for tornado formation.

The change in wind speed and direction with height is known as wind shear. This wind shear is linked to the eventual development of rotation from which a tornado may form.

A tornado is formed when a thunderstorm occurs. The most common type of thunderstorm for forming a tornado is the supercell. Thunderstorms develop when the air becomes warm and moist, in advance of cold fronts that move eastwards. These are the thunderstorms that usually produce strong winds, large sized hail, and tornados. When both high pressure and low pressure air interact with each other, the low pressure draws in high pressure air to form the vortex and eventually results in a tornado. Tornadoes can also accompany hurricanes and tropical storms that move over the land.

Horizontal winds begin rolling

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

Rising air tilts the rotating air from horizontal to vertical

Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical

Most strong and violent tornadoes form within this area of strong rotation.

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.


A third layer of hot dry air becomes established between the warm moist air at low levels and the cool dry air aloft. This hot layer acts as a cap and allows the warm air underneath to warm further. making the air even more unstable. Things start to happen when a storm system aloft moves east and begins to lift the various layers. Through this lifting process the cap is removed, thereby setting the stage for explosive thunderstorm development as strong updraft's develop.

Complex interactions between the updraft and the surrounding winds may cause the updraft to begin rotating and a tornado is born. When this happens, the cold air starts sinking down, resulting in the warm wind whirling upward, spinning faster and faster, and forming a high column. When the upward moving winds are strong enough, it can go up to 10 miles in height, and even more, spinning at speeds measuring up to 100 mph. These spinning winds create powerful storm clouds, which occur at a height of 70,000 feet, often stretching 10 miles in width.

The tornadoes that occur in the winter or early spring generally are associated with strong weather conditions that are created in the central states, which then move eastward. Sometimes, this kind of weather pattern creates a large number of tornados. A number of states can be affected by several powerful thunderstorms as well as tornados.

To sum it up, tornadoes can be attributed to:

tornado
  • Instability
  • Moisture
  • Wind Shear
This explains why the United States experiences the largest number of tornadoes in the world, followed by the Indian subcontinent. Notable tornadoes in Kansas include the Udall,Kansas tornado on May 25,1955. It was reported that there was a tornado watch but it had been canceled by the local media an hour and a half before the tornado hit. A large F5 tornado hit during the night, injuring 270 and killing 83. More recently was the May 4, 2007, EF5 Tornado that hit Greensburg, Kansas. Where an EF5 tornado destroyed 95 percent of the town with wind speeds of near 205 miles per hour. At least 60 people were injured and 10 people died in the city limits. The destruction caused by these tornadoes in itself can give you a rough idea of how dangerous they can be."