Clouds are visible concentrations of small water or ice particles that form through the condensation of water vapor. Clouds are classified based on their appearance and their distance from the ground. Some clouds bring rain and snow while others just visually sit in the sky and produce no precipitation.
High-level clouds form 20,000 feet above the ground and include cirrus, cirrostratus and cirrocumulus. These types of clouds are easily recognized by their widespread concentration and wispy, gossamer or lumpy appearance. They are composed of ice crystals. At sunset, these clouds may reflect a variety of colors.
Mid-level clouds form 6,500 to 20,000 feet above ground and include altostratus and altocumulus. Their composition depends on height, time of year and temperature, so they can be made of water, ice or both. Altostratus clouds appear flat and disconnected while altocumulus clouds are more puffy and have connections to each other.
Low-level clouds form below 6,500 feet and include stratocumulus and nimbostratus. They are generally made entirely of water. Both types of clouds produce rain and are the clouds that produce gray skies. Stratocumulus clouds appear as layers of puffy, clumpy clouds with varying thickness. Nimbostratus clouds are thick clouds that bring rain and snow.