Before you panic at that low-hanging cloud, take a closer look, it might just be a harmless scud cloud.

Scud clouds are small, ragged-looking clouds that form just beneath a larger cloud base, often giving the sky an ominous or unsettled appearance. Unlike organized storm clouds, scud clouds hang out individually and can appear scattered or wispy. They're frequently mistaken for funnel clouds because of their shape and low altitude, especially when the wind is pushing them quickly across the horizon. But scud clouds do not rotate and aren't dangerous on their own.

Scud clouds are simply smaller clouds that hang beneath the main storm cloud. They often give the base of the storm a ragged appearance, and while some are small and wispy, others can hang quite low. Because of their shape and position, it’s easy to see why people sometimes mistake them for tornadoes!

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In the 19th century, scud clouds were often called “water-dogs”, a term some still use today. Traditionally, spotting water-dogs in the sky was seen as a sign that more rain was on the way. So whether you're using the old-school nickname or the more modern meteorological term, keep an eye out for these quirky cloud formations the next time a thunderstorm rolls in, they might just be the sky’s way of signaling what’s coming next.

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.