Classification of Clouds
In 1803 a London man, Luke Howard, proposed the first classification system of clouds. (Taylor, 168) Clouds are classified into different groups based on the height of the cloud's base above the surface of the Earth. They are also classified by the way they look from the ground. Clouds are a good indicator of what weather is coming. There are three basic clouds of shapes which include cumulus meaning "mound", stratus meaning "spread out" and cirrus meaning "curly". (Simon, 1993) Simon also mentions a few other words that are associated with clouds are nimbus (rain cloud), cirro (high cloud), and alto (mid-level cloud). (1993) When two of the words are combined, that means that the cloud shares properties of both.
This chart shows the categories of clouds and what their heights are in the sky.
High Clouds
This grouping consists of Cirrus, Cirrostratus, and Cirrocumulus clouds. These clouds are made of ice crystals because cold air that is in the upper area of the sky. (Hatheway, 2007)
Cirrus Clouds
Cirrus clouds are wispy, feather-like, and entirely made of ice crystals. Cirrus clouds are very thin and at times the only way to notice them in the sky is by seeing a "halo" around the sun or the moon. (Taylor, 170) Cirrus clouds can appear straight, have a comma shape to them, or seem tangled within each other. These clouds are usually in the sky during fair weather. They point in the direction the air is moving. (Bramer, Hall, and Wojtowicz, 2010) These clouds are good indicators that a warm front is in the forecast.
Cirrostratus Clouds
Cirrostratus clouds are also thin with a whitish veil that extends across the sky. (Taylor, 173) The sun and moon can be seen through these clouds, which is why many people describe these clouds as "sheet like." ("Cloud Types," 2000) This means the sun, moon, and even stars can be seen through this thin layer of clouds. Halos are usually present with Cirrostratus clouds also.
Cirrocumulus Clouds
Cirrocumulus clouds are most often white, small, and round puffs. Occasionally these clouds may appear to be gray. When these clouds cover a lot of the sky, it is known as a "mackerel sky" because it resembles scales of a fish. (Hatheway, 2007) Cirrocumulus clouds are uncommon, and the best way to identify them is if cirrus clouds are obvious. (Taylor, 173)
Middle Clouds
This group consists of Altocumulus and Altostratus clouds. These clouds are formed by drops of water and ice crystals. (Hatheway, 2007) These clouds are associated with active fronts of weather. (Taylor, 175) Middle clouds are common in tropic regions. These two clouds usually merge together in the sky.
Altocumulus Clouds
Altocumulus clouds are a grayish-white color with one part of the cloud being darker than the other. (Hatheway, 2007) When these clouds are seen, a thunderstorm can usually be expected. These clouds occur beneath high level inversions of the atmospheres. (Taylor, 175)
Altostratus Clouds
Altostratus clouds cover the entire sky with a gray or blue color to them. These clouds can appear watery of fuzzy when the sun or moon shines through them. (Hatheway, 2007) Formation of these clouds usually occur before storms and are likely to produce snow or rain. A corona often surrounds the sun or moon when these clouds appear. A corona is a wreath of light that are slightly larger than the sun or moon. (Taylor, 175)
Low Clouds
This group consists of Stratus, Stratocumulus, and Nimbostratus clouds. These clouds consist of water droplets. They are gray and cover most or all of the sky. (Hatheway, 2007) These clouds appear very smooth. (Taylor, 179) A light mist or drizzle will usually occur.
Stratus Clouds
These clouds are associated with overcast weather. (Barker, 2002) Fog or mist results from these clouds. When more precipitation comes from these clouds they change from being titled stratus to nimbostratus. Formation of these clouds occurs when there is a weak air that lifts another layer of air high enough to start condensation. (Barker, 2002) These clouds are very low and look broad and thin. (Simon, 1993) "Ground fog" usually takes place late at night or early morning with these clouds, however when the sun does come up the fog "burns off." (Simon, 1993)
Stratocumulus Clouds
Stratocumulus clouds are low layers of clouds that look lumpy and vary from dark gray to light gray. (Bramer, Hall, and Wojtowicz, 2010) Precipitation does not usually occur when these clouds are visible.
Nimbostratus Clouds
Nimbostratus clouds are dark clouds with bases that are rough and rigid. (Hatheway, 2008) Usually the forecast is calling for rain or snow when these clouds are seen. The sun and moon are not visible through nimbostratus clouds. Usually it is hard to determine these clouds because of a layer of fog that forms under and around these clouds. (Bramer, Hall, and Wojtowicz, 2010)
Contrails
When jets or airplanes high in the sky have streaks coming out of their jets, it is considered to be Contrails. (Hatheway, 2008) These are still considered to be clouds because they are still formed by water vapor. This water vapor is condensed and frozen that exist around the exhaust. Evaporation can occur quickly or can take some time. Hathway mentions that some consider contrails to be human made cirrus clouds. (2008) There are three types of contrails which are short lived, persistent non-spreading and persistent spreading. (Hatheway, 2008)