What happens in the atmosphere when there is a tornado?

Tornadoes form during thunderstorms. These storms usually developing a warm, moist air mass ahead of a cold front (where cold air moves in) or dry line (where dry air moves in). Within the storm air rises rapidly in a strong updraft. The rising air cools causing the moisture to condense and release energy. At the same time, regional winds change significantly in speed and direction with height. This causes the updraft of the storm to rotate. It is form this rotation that the smaller, more intense circulation of a tornado may form.

Within the tornado itself air spirals inward and upward rapidly around a center of intense low pressure. Because of the pressure drop air cools within the tornado, causing moisture to condense to form the visible funnel.