Wx Savvy |

Gray Clouds vs. White Clouds

Some clouds appear gray simply because the cloud is blocking the sunlight.

Imagine you are standing directly underneath a tall cumulus cloud. Very little sunlight from above can penetrate down through the thick cloud, so from underneath the cloud it looks dark. Sunlight has to travel thousands of feet through the cloud to our eyes. As the light travels through a cloud it gets scattered, absorbed and reflected. That scattering, absorption and reflection reduces the amount of sunlight that will eventually make it through the cloud and to our eyes.

The thicker the cloud,the less light that will reach our eyes. Notice the thick and dark clouds in the picture below.

If you are under a tall dark cloud, wait until it passes and look at it again. The side of the cloud will be illuminated by sunlight and the cloud will appear bright and white. In the picture below, the tall cloud appears white only because the picture taker is not standing underneath a cloud.

However,if you walked underneath this cloud it would look much darker.

So, the brightness of the cloud (white versus gray) has a lot to do with both where you are standing and the thickness of the cloud cover.

There are times that the cloud is not tall, but is more like a blanket covering the sky. In those cases all you'll see all gray skies and the afternoon will seem much darker than usual. This is of course because not much sunlight is making it through that blanket of clouds.

However, if you were to fly a plane above the blanket of clouds, you would see all white. You'll notice how bright and white the clouds are in the picture below, which was taken from an airplane. That's because the sunlight is unhindered and reflecting off of the tops of the clouds, illuminating the now white blanket of clouds.

Some clouds are thin, and they appear more white than gray because there is less cloud to block the sunlight. Below is an example of some rather thin clouds.

Notice that I am not talking about color, but rather about the brightness of clouds. That's because gray clouds are due to the brightness of sunlight scattered and reflected by the cloud. If you're curious as to why clouds are white to begin with you can learn more by clicking here