How are cloudy days formed?

The weather changes on the earth's surface are related to many factors, such as sunlight exposure, atmospheric changes, topographic effects, etc.

Cloud is an important factor in the weather, which is formed by the accumulation of water vapor evaporated from the surface or rivers, lakes and oceans.

When the thickness of the cloud is thin and the distance between clouds is large, it will generally appear white, which is the true color of water vapor.

When the clouds are thick and dense, it is difficult for sunlight to reach the ground through the clouds. Seen from the ground, the clouds were dark and turned into dark clouds.

In fact, from the plane, the dark clouds below are still white.