A tornado is a violently rotating column of air extending from a thunderstorm to the ground.
Most tornadoes develop from severe convective storms, especially supercells with a persistent rotating updraft called a mesocyclone. A visible funnel cloud is made of condensed water droplets, but the rotating air can extend beyond the visible funnel. A tornado is classified as such when the circulation reaches the ground, whether or not a complete funnel is visible.
Tornadoes differ from hurricanes in scale and structure. A hurricane is a large tropical cyclone that forms over warm ocean water, while a tornado is much smaller and usually develops from a thunderstorm. Tornado intensity is estimated from damage surveys using the Enhanced Fujita scale rather than directly assigning a rating from the funnel’s appearance.