Breakdown: Why storm clouds usually appear dark

Breakdown: Why some clouds appear darker

MEMPHIS, Tenn. (WMC) - Often times when we look at the clouds they are white but before a storm you may notice that the clouds will get darker or more gray and dreary.

Clouds form when the air close to the ground warms it will begin to rise and within that rising air it contains water vapor. As the air rises it cools and the water vapor within the rising air will condense onto dust particles in the air. The water vapor or ice crystals coalesce, or come together, to form clouds.

The particles in the atmosphere scatter more blue light than other colors which is why the sky appears blue but the small particles of clouds, scatter all the colors of light equally, which make up white light.

So the gray hue is all about how thick the clouds are and how high up they are. The larger the water drops the more gray and the droplets are the biggest right before they fall as rain or snow. This is because light gets absorbed versus being scattered, which means less light getting through.

That is, a cloud gets thicker and denser as it gathers more water droplets and ice crystals — the thicker it gets, the more light it scatters, resulting in less light penetrating all the way through.

This effect becomes more pronounced the larger the water droplets get — such as right before they’re large enough to fall from the sky as rain or snow — because they become more efficient at absorbing light, rather than scattering it.

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