On Cloud 9 By emma pappas

Main types of clouds

Stratus clouds are low-level clouds with base height ranging from 0-6,500ft (2,000m) characterized by horizontal layering with a uniform base, with atmospheric stability. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region. While light rain may fall, this cloud does not indicate much meteorological activity.


Cumulonimbus clouds are dense towering vertical clouds associated with thunderstorms and atmospheric instability, forming from water vapor carried by powerful upward air currents. Has a base height from 1,100-6,500 ft (1,981 m) reaching 40,000 ft (12,000 m), extending from low to high regions.


Cumulus clouds are often precursors of other types of cloud, such as cumulonimbus, when influenced by weather factors such as instability, moisture, and temperature gradient. Normally, cumulus clouds have a stable atmosphere and produce little or no precipitation, but they can grow into the precipitation-bearing congestus or cumulonimbus clouds. The height of the base ranges from 1,200-6,600 ft (2,000 m). Three types:

Cumulus humilis cloud

Has an altitude of 500-3000 m (1,500-10,000 ft) with little vertical extent that is commonly referred to as "fair weather cumulus" and common in the summer. Precipitation is uncommon due to the stability of the atmosphere. Wider than they are tall.

Cumulus mediocris clouds

Has an altitude of 500-3000 m (1,500-10,000 ft) and larger in vertical development than cumulus humilis. Are as wide as they are tall. These clouds do not generally produce precipitation of more than very light intensity due to stability, but may further advance into clouds such as cumulus congestus and Cumulonimbus, which do.

Cumulus congestus clouds

Has an altitude up to 6,000 m (up to 20,000 ft). Cumulus congestus clouds are characteristic of unstable areas of the atmosphere which are undergoing convection and light precipitation is common. They are often characterized by sharp outlines and great vertical development.


Low-level clumps or patches of cloud varying in colour from bright white to dark grey. They normally have well defined bases and some parts much darker than others. Stratocumulus clouds can be present in all types of weather conditions, from dry settled weather to light rain and snow. Weak convective currents create shallow cloud layers because of drier, stable air above preventing continued vertical development. Base ranges from 1,200 - 8000 ft (2,400 m).


Nimbostratus was formerly a low-level stratiform genus that is now classified by the World Meteorological Organization (WMO) as a vertical or multi-level stratus type. Nimbostratus usually produces precipitation over a wide area, due to instability in the atmosphere. It has a diffuse cloud base generally found anywhere from near surface in the low levels and about 3,000 m (9,800 ft). Extends from low to mid region of the atmosphere.


Has an altitude of 2,000–6,100 m (6,500–20,000 ft). Similar to cirrocumulus, but individual segments are larger and darker. There is no precipitation due to atmospheric stability. However, if the layers become tufted in appearance due to increased airmass instability, then the altocumulus clouds become more purely cumuliform in structure.


Has an altitude of 2,400–6,100 m (6,500–24,000 ft). Altostratus is formed by the lifting of a large mostly stable air mass that causes invisible water vapor to condense into cloud. It can produce light precipitation, often in the form of virga. If the precipitation increases in persistence and intensity, the altostratus cloud may thicken into nimbostratus.


It forms when water vapor undergoes deposition at altitudes above 5,500 m (18,000 ft) in temperate regions and above 6,400 m (21,000 ft) in tropical regions. It also forms from the outflow of tropical cyclones or the anvils of cumulonimbus cloud. Since cirrus clouds arrive in advance of the frontal system or tropical cyclone, it indicates that weather conditions may soon deteriorate because of atmospheric stability. While it indicates the arrival of precipitation , cirrus clouds only produce fall streaks (falling ice crystals that evaporate before landing on the ground).

Cirrus fibratus clouds

Altitude above 6,000 m (Above 20,000 ft). Like other cirrus clouds, cirrus fibratus occur at high altitudes. They can indicate an approaching warm front, however, they can also be an indication that fair weather will follow. No precipitation due to stable atmosphere.

Cirrus uncinus clouds

Altitude above 7000 m (Above 23,000 ft). The clouds occur at very high altitudes, at a temperature of about −50 to −40 °C (−58 to −40 °F). They are generally seen when a warm front is approaching, and stable resulting in no precipitation. They are very high in the troposphere and generally mean that precipitation, usually rain, is approaching.


A cloud of a class characterized by a composition of ice crystals and often by the production of halo phenomena and appearing as a whitish and usually somewhat fibrous veil, often covering the whole sky and sometimes so thin as to be hardly discernible with a high altitude, about 20,000–40,000 feet (6000–12,000 meters). Stable atmosphere so no precipitation, but usually signal the approach of a warm front.


Has an altitude of 6,000-12,000 m (20,000-40,000 ft). Like lower altitude cumuliform and stratocumuliform clouds, cirrocumulus signifies convection from atmospheric instability. Unlike other high cirrus and cirrostratus, cirrocumulus includes a small amount of liquid water droplets, although these are in a supercooled state. This can produce precipitation in the form of a virga consisting of ice or snow.

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