That’s one of the most common questions I hear when making weather presentations.
It is also one of the simplest to answer…
The color of a cloud is determined by how much light is reflected from it.
Here are 3 examples where the color of a cloud, combined with the thickness of that cloud, can give you some idea of what’s going on weather-wise in the skies behind it.
Scattered Cumulus Clouds
On a day when the sky is mainly sunny – with just a few puffy cumulus clouds around – the clouds appear white.
For the most part, the sun’s rays can penetrate these small clouds – so they appear white on the top, side and bottom.
But even these clouds have a bit of a blue-ish tint on the bottom, indicating a bit of blocking of the sun’s bright rays.
Building Cumulus Clouds
In this next photo, notice the side of the building cumulus clouds facing the sun appear bright white (actually a bit pink), but the side of the clouds away from the sun are dark.
We can assume the sun is low in the sky to the left of the photo. Now you can start to see how the sun’s rays – as bright as they are – have trouble penetrating a thick cloud. The part of each cloud not illuminated directly by the sun appears dark.
Towering Cumulus Clouds
Now, let’s apply this to a towering cumulus cloud, the kind which brings heavy rain.
In this photo, it’s apparent the cloud is so thick and full of water that the sun’s light simply cannot reach the bottom of the cloud. No light means dark.
Generally speaking, the taller (or thicker) the cloud, the darker the bottom is going to appear. Meteorologically speaking, the taller (or thicker) the cloud, the more moisture it has inside and the heavier the rain is going to be that falls from that cloud.
Big thunderstorms can be well over 50,000 feet tall. If you get caught under something that massive, it’s going to look like night.
More Fun Cloud Stuff
I'm a TV weatherman in south Texas. I get blamed for the bad weather, but I also get credit for the beautiful days. I absolutely love my job!