HIGH POINT, N.C. (WGHP) — When there are dark clouds on the horizon, you know that a storm is coming — but why?

Kenn from Mount Gilead wrote in to ask, “I’ve always wondered, why are some clouds white, some gray, and others dark gray to even black? What causes the different colors of the clouds?”

The reason some clouds appear to be white and some look to be near-black has to do with the thickness of the cloud.


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According to NOAA, clouds are made of water droplets that reflect the sunlight. So, when the light passes through a cloud, the water droplets scatter all colors of light. When light contains all colors, it appears white to our eyes.

As clouds thicken and grow taller, sunlight is not able to pass through the cloud as easily and this gives the cloud a gray color.

An example of a gray cloud is a nimbostratus cloud. A nimbostratus cloud is a type of rain cloud. Since it’s a rain cloud, it contains more water droplets in it making it harder for sunlight to pass through the cloud. When the water droplets aren’t able to scatter as much light due to the thickness of the cloud, it appears gray.

The skyline of the City of Greensboro on two very different cloudy days. (WGHP)

As a cloud continues to grow in height and thickness, it can even appear almost black. An example of a nearly black cloud is a cumulonimbus cloud, or a thunderstorm cloud. The stronger a thunderstorm, the taller and thicker the cloud usually is.


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This means a cumulonimbus cloud has so many water droplets inside of it that very little sunlight is able to pass through it. This makes it appear as a dark, black cloud.

This also means the stronger the thunderstorm, the more likely it is for a nearly black storm cloud.

If you or your child have a weather-related question, let us know using the form on our “Ask Alex!” page. Meteorologist Alex Schneider joined the FOX8 Max Weather Team in August 2022. She has a bachelor of science in atmospheric science and meteorology from the University of North Carolina at Asheville.