Which of the following causes tornadoes?

Conditions suitable for the formation of a tornado develop when varying temperatures and humidity come together and form thunderclouds. This refers to the presence of warm and moist condition in the lower atmosphere and cold and dry conditions in the upper atmosphere. The place where these varying masses of air meet is known as the dry-line. Such conditions, which are suitable for the formation of a tornado, are most often observed just before a low pressure system develops.

Once the ideal conditions occur, the warm air tries to rise in the atmosphere, while the cold air blocks it. This makes the air in between rotate horizontally. In the meanwhile, the land is heated by the Sun, and hence, the air near the ground becomes warm and starts rising. Continuous fueling by the heat energy from the Sun ensures that the warm air has an upper hand over cold air. As a result of this, the cold air at the top starts sinking and the warm air below starts rising in a spinning motion. As the amount of warm air increases, the formation gains height and becomes intense. The intensity of these devastating tornadoes is such that they can clear off anything that comes in their path.