Different types of clouds are symptomatic of different environmental conditions. Clouds are given names based on their shapes, altitudes, and whether or not they are able to produce precipitation. The system used for naming clouds was created by a British chemist and amateur meteorologist named Luke Howard in 1802. He wasn't the first person to try to come up with a way of categorizing and identifying clouds, but his system was simple enough that it is still in use today. He defined a few cloud types, gave them Latin names, and treated the naming of clouds similar to the Linnean taxonomy system used to name species. His basic cloud names were "nimbus," "cumulus," "stratus," and "cirrus," and combined with other Latin prefixes as needed to create more precise names. The ability to identify cloud types is a helpful tool for predicting the weather and detecting the approach of incoming fronts.

Clouds Under 2000 Meters

The first group of clouds consists of cumulus, stratus, stratocumulus and cumulonimbus clouds. Though many people don't think of it as a cloud, fog is also included in this group. These are low-level clouds, which means that their bases are at altitudes under 2000 m. The name cumulus describes a fluffy, piled appearance. These clouds are the cottony clouds that appear during fair weather. Stratus describes a broad, sheetlike appearance-- the kind of clouds seen on an overcast day. They can look white or gray, and may even obscure the sun. Nimbus clouds are clouds that produce precipitation. Stratocumulus combines the characteristics of stratus and cumulus clouds-- they make the sky appear overcast, but are puffy rather than uniform in appearance. Cumulonimbus clouds are piled-up clouds that create precipitation. They appear when the weather is warm and humid, and can produce thunder, lighning, rain, tornadoes, hailstorms, and other severe weather. Nimbostratus clouds are smooth, uniform clouds that produce rain, freezing rain, or snow. Fog is simply a cloud that sits right at ground level.

Clouds Between 2000-4000 Meters

The second group of clouds consists of nimbostratus, altostratus and altocumulus clouds are mid-level clouds. These are mid-level clouds, which means that their bases sit at altitudes between 2000-4000 m. The prefix "alto" denotes that these are mid-level clouds. Altostratus clouds are mid-level stratus clouds. They are uniform, and can give the sky a grayish or bluish-gray cast. They may not obscure the sun, and instead give the sky a "frosted glass" appearance. Altocumulus clouds are mid-level cumulus clouds. Because of their altitude, they can appear as ripples or waves instead of cottonlike puffs like they do below 4000 m. Oftentimes, these clouds appear with weather fronts and may indicate that rain is on the way.

Clouds Over 6000 Meters

The third group of clouds consists of cirrus, cirrocumulus, and cirrostratus clouds, as well as the streaky contrails left by jets. These are high-level clouds, which means that their bases sit at altitudes over 6000 m. These clouds are denoted by the prefix "cirro-", and have a uniquely fuzzy, indistinct appearance due to being primarily composed of ice crystals. Cirrus clouds look like curls of hair. They are thin, wispy, white clouds with patches of sky visible through them. Cirrostratus clouds are high, uniform stratus clouds. These clouds can create halos around the sun or moon due to the way their ice crystals refract light. Cirrocumulus clouds are high-level cumulus clouds. These clouds often have a wavy, patchy, or herringbone pattern. Even though contrails aren't a natural phenomenon, they're still a type of cloud. When water vapor leaves a plane's exhaust at a high elevation, it can combine with water vapor and ice crystals in the atmosphere, freeze into more ice crystals, and form long, streaky clouds. Contrails can be used to tell some things about the weather when they were formed. If the air is too dry, no contrails will form. If there's a little moisture, contrails may form and quickly evaporate. Humid air can result in contrails that expand into long, puffy trails and last for a long time after the plane has passed.

Other Types

Sometimes, more than one type of cloud may appear in the sky at a time. These may be the same type of cloud at different levels, like the appearance of stratus and cirrostratus clouds. They may also be different types of clouds that signal the edge of a front. Stratus and stratocumulus clouds can make it difficult to determine if there are clouds present at other altitudes-- since they obscure so much of the sky at a low level, it is nearly impossible to spot mid- or high-level clouds without specialized instruments.

Identifying types of clouds isn't the only way to determine at what altitude clouds are. The presence or absence of precipitation is a helpful indicator. Only low-level clouds generally produce precipitation, with precipitation becoming more rare the higher clouds are. The opacity of stratus clouds changes with altitude, as well. Lower-level clouds tend to be more opaque than higher-level clouds, which is why stratus clouds may obscure the sun while cirrostratus clouds produce colorful halos and a frosted glass appearance. Lastly, the altitude of certain types of clouds can be estimated by their size. The larger a cumulus cloud is, the closer it is to the ground.