The Earth’s troposphere is the lowest level of our atmosphere and this is where clouds hang out. All air contains water. The water in the air near the ground is in vapor form. When warm air rises, it expands and cools. Cool air holds less water vapor than warm air, so some of the vapor condenses onto microscopic dust particles in the air turning into water or ice. The water droplets are so small and light they float in the air. When billions of droplets combine, they become a visible cloud.
Clouds are white because they reflect the light from the sun. The rays from the sun are made up of red, orange, yellow, green, blue, indigo and violet. When you add those colors together, the result is white. Clouds reflect all of the sunlight’s colors the exact same amount, so they appear white.
Clouds are classified by the height of the cloud base. Names beginning with "Cirr" are located at high levels. Alto clouds are found at middle levels. Stratus clouds are at low levels.
High-Level Clouds form above 20,000 feet and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. They are typically thin and white in appearance, but can appear in an array of colors when the sun is low on the horizon.
Mid-Level Clouds typically appear between 6,500 to 20,000 feet. Because of their lower altitudes, they are composed primarily of water droplets. They can also be composed of ice crystals when temperatures are cold enough.
Low-Level Clouds are mostly composed of water droplets since their bases generally lie below 6,500 feet. When temperatures are cold enough, these clouds may also contain ice particles and snow.
Vertically-Developed Clouds are commonly generated through either thermal convection or frontal lifting. They can grow to heights in excess of 39,000 feet, releasing energy through the condensation of water vapor within the cloud itself.
Cirrus clouds are the most common of the high clouds. They are composed of ice and are thin, wispy clouds blown in high winds forming long streamers. Cirrus clouds are usually white and predict fair to pleasant weather. By watching the movement of cirrus clouds you can tell from which direction weather is approaching. Cirrus clouds usually indicate that a change in the weather will occur within 24 hours.
Cirrostratus clouds are thin, sheet-like high clouds that often cover the entire sky. They are so thin that the sun and moon can be seen through them. Cirrostratus clouds usually come 12-24 hours before a rain or snowstorm.
Cirrocumulus clouds appear as small, rounded white puffs that appear in long rows. Their small ripples sometime resemble the scales of a fish. Cirrocumulus clouds are usually seen in the winter and indicate fair, but cold, weather. In tropical regions, they may indicate an approaching hurricane.
Altostratus clouds are gray or blue-gray mid level clouds composed of ice crystals and water droplets. These clouds usually cover the entire sky. In the thinner areas of the clouds, the sun may be dimly visible as a round disk. Altostratus clouds often form ahead of storms with continuous rain or snow.
Altocumulus clouds are mid level clouds made of water droplets and appear as gray puffy masses usually in groups. If you see altocumulus clouds on a warm, sticky morning, be prepared to see thunderstorms late in the afternoon.
Stratus clouds are uniform grayish clouds that often cover the entire sky. They resemble fog that doesn't reach the ground. Light mist or drizzle sometimes falls out of these clouds.
Stratocumulus clouds are low, puffy and gray and most form in rows with blue sky visible in between them. Rain rarely occurs with stratocumulus clouds, however, they can turn into nimbostratus clouds.
Nimbostratus clouds form a dark gray, wet looking cloudy layer associated with continuously falling rain or snow. They often produce precipitation that is usually light to moderate.
Cumulus clouds are white, puffy clouds that look like pieces of floating cotton. Cumulus clouds are often called "fair-weather clouds". The base of each cloud is flat and the top has rounded towers. When the top of a cumulus cloud resembles the head of a cauliflower, it is called cumulus congestus or towering cumulus. These clouds grow upward and they can develop into giant cumulonimbus clouds, which are thunderstorm clouds.
Cumulonimbus clouds are thunderstorm clouds. High winds can flatten the top of the cloud into an anvil-like shape. Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning and even tornadoes. The anvil usually points in the direction the storm is moving.
Mammatus clouds are low hanging bulges that droop from cumulonimbus clouds. Mammatus clouds are usually associated with severe weather.
Lenticular clouds are caused by a wave wind pattern created by the mountains. They look like discs or flying saucers that form near mountains.
Fog is a cloud on the ground composed of billions of tiny water droplets floating in the air. Fog exists if the atmospheric visibility near the Earth's surface is reduced to around three quarters of a mile.
Contrails are condensation trails left behind jet aircrafts. Contrails form when hot humid air from jet exhaust mixes with environmental air of low vapor pressure and low temperature. The mixing is a result of turbulence generated by the exhaust.
Green Clouds are often associated with severe weather. They form when the clouds are illuminated by light reflected off green vegetation, such as large cornfields or a heavily wooded forest. In the Great Plains region of the U.S., green clouds are associated with storms likely to produce tornadoes.
Cumulus — Heap
Stratus — Layer
Cirrus — Curl of Hair
Nimbus — Rain
Now you’re a little smarter, Girlfriend — And so am I.