For most people, seeing what looks like a tornado crossing the horizon, you would bet your money that it was an actual tornado. But many times it’s nothing more than a funnel cloud. Funnel clouds look like tornadoes, and form in the same way tornadoes do - the only difference is this: funnel clouds do NOT touch the ground.

A funnel cloud is a rotating, funnel-shaped column of air that extends from the base of a cloud but does not touch the ground. It often looks like a thin, rope-like or cone-shaped cloud dangling from the sky. These formations are usually associated with severe thunderstorms and are a visual sign that powerful weather is underway.

On their own, funnel clouds are not dangerous, since they haven’t reached the ground. But they are important to watch because if a funnel cloud touches the ground, then it officially becomes a tornado, which can cause serious damage. That’s why trained spotters and radar technology are used to monitor these features closely.

Such a small difference can mean the difference between a harmless, gnarly looking cloud, and a powerful force of nature that can cause extreme damage and loss of life.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.