Clouds move due to wind currents that carry them through the lower levels of Earth's atmosphere. Even if there is no wind felt at ground level, wind constantly blows through the atmosphere carrying clouds, air particles and dust with it.
Clouds are very similar to fog. They are composed of tiny water droplets and air particles that stick together to form large, billowy, white or gray structures. Clouds form whenever warm, moist air rises through the atmospheric layers and cools with the lowering atmospheric pressure.
Clouds form different shapes, which meteorologists have studied and classified. Different cloud shapes indicate different atmospheric and weather conditions. Color is also significant, and can be a strong and obvious predictor of pending weather.
The color of clouds is determined by the amount of water they contain. Dark gray and black clouds contain a great deal of water and are an indicator of pending rain. On the other hand, white and fluffy clouds have very little water and indicate dry weather.
Regardless of shape or color, all clouds move with the wind. Most clouds are observed moving in the troposphere closest to Earth, though there are also clouds in the much higher stratosphere and mesosphere.