PACIFIC WEATHER | CARIBBEAN WEATHER | ATLANTIC WEATHER | CLIMATOLOGY  |LIGHTNING DENSITY | CLOUDS

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TEN MAIN CLOUD TYPES

 

stratus

—found in the low levels of the atmosphere, tend to produce a light drizzle; Stratus (St): 0 to 500 m altitude

It is a cloud of grayness, which forms a uniform, extended and gray layer of low clouds, which can occur to drizzle, snow or ice prisms. It can also take the form of a shredded bench when it dissipates. Its irregular contours and dimensions change continuously and rapidly. Its base is very low (between 20 and 500 m) and it can hide the peaks of small hills. When it touches the ground, it turns into a fog. They are particularly common in large urban areas because of air pollution.

Effect It can produce drizzle, granular snow or snow in very small flakes, in very small quantities and with very low intensity.

 

altostratus

—(‘alto’ meaning high), found in the middle level, tend to be very good rain producing system for large areas across continents, particularly inland; 2 to 6 km altitude

It is a bluish or greyish cloud layer with a striated, fibrous or uniform appearance and covers a large part of the sky. It can let the sun appear where it is thinnest. It looks like a cirrostratus, but without the halo phenomenon. Several layers of altostratus can overlap at intervals of a few dozen metres and are often associated with altocumulus.

Effect When thick, it can bring rain, snow or ice granules.

nimbostratus

—formed when altostratus undergoes further vertical development, allowing the cloud to hold more moisture, and causing the cloud base to lower and produce heavier rainfall; also appears darker in color; 2 to 6 km altitude

It is a sign of bad weather and takes the form of a thick grey and dark cloud layer, whose appearance is blurred by the precipitation it generates. Coming from the altostratus, it causes either rain or snow continuously with a strong to very strong intensity. It often gives the impression of being lit from the inside, but is thick enough to completely hide the sun. It is regularly accompanied by shattered low clouds (pannus).

Effect Rain and rains can last all day and in winter, if it is cold, it will generate snow or ice pellets.

 

cirrostratus

—found in the higher levels of the atmosphere, white and wispy, and made of ice crystals. Often produces a lot of halo activity with cirrostratus cloud, with the ice crystals refracting light around the moon and the sun. 5 to 13 km altitude

Appears as a transparent, whitish cloud veil with a fibrous and smooth appearance and partially or entirely covers the sky, yet it is not thick enough to remove cast shadows. In general, it is associated with a halo phenomenon. Composed of small, widely dispersed ice crystals,  announces a change in the weather.

Effect Precipitation: It never produces precipitation. It is often found at the front of a warm front and may precede precipitation up to 24 hours after its appearance.

in the lower part of the atmosphere clouds are

cumulus

—low level cloud which tends to produce short duration, fairly intense rainfall that is often very localized, meaning that rain falling at your house might not be falling at your next bay a mile up the coast  200 m at 2 km altitude

Cumulus is a cloud of good weather despite its imposing size and develops vertically. It is dense, with well defined contours. Their upper side buds and often resembles a cauliflower. When the sun shines on them, they are bright white, while their rather flat base is more or less dark. We distinguish 3 varieties of cumulus according to their vertical development.

Effect The cumulus of good weather does not announce rain but it sometimes gives rise to rain, snow or rolled snow, always in the form of rainfall.

 

 

stratocumulus

—found in the lower levels, a blend between stratiform and cumuliform cloud and taking on appearances from both these cloud types, may produce drizzle;  300 m at 2.5 km altitude

Marine stratocumulus is a type of stratocumulus cloud that form in the stable air off the west coast of major land masses. The Earth spins on its axis, which results in the Coriolis force pushing the ocean surface water away from the coast in the mid-latitudes. This results in upwelling of cold water from below that creates a pool of cool water at the surface, which in turn cools the air directly above it. The surface cooling results in a large temperature inversion at the top of the marine layer. As the temperature is cooled to the dewpoint, water vapor condenses upon available cloud condensation nuclei, and forms a cloud. The stability of the marine layer prevents deep convection, and thus stratiform clouds are formed

Effect They announce a rather threatening weather and it can – but very rarely – give rise to light rainfall, snow or rolled snow.

 

 

 

altocumulus

—found in the middle levels, looks like sheep in the sky, may produce light showers; 2 to 6 km altitude

Form of a bench or layer of clouds in the form of white and/or grey strips, pebbles or rollers. They can be welded together and are mainly composed of super cooled water droplets.

Effect do not announce a particular weather but rather a change of weather. They can bring rain in rather light and short rainfalls.

 

 

cirrocumulus

—small, rippled, higher level cloud, does not produce precipitation; 5 to 13 km altitude

small white clouds in the form of granules or wrinkles that form a bench, a layer or a thin layer, letting the sun filter. Essentially composed of ice crystals, they follow the cirrus and cirrostratus and announce a change in weather.

Effect They do not announce any particular weather and very rarely give rainfall that never reaches the ground.

 

 

cumulonimbus

—the largest cloud of all, forms in the lower layer of the atmosphere but extends through all three layers right to the top of the atmosphere. Also known as thunderstorm cloud, producing thunder and lightning. 300 m a 17 km

These are cumulus clouds which predict  bad weather: storms, showers, hail. They are formed by enormous volutes at the top and can generate very violent bad weather. These are the only clouds that cause thunderstorms.

Effect It brings the most violent bad weather, in winter as in summer: rain, snow, rolled snow, sleet and hail, always in the form of showers, often accompanied by lightning and thunder. Sometimes it can even form a waterspout, or even exceptionally, a tornado that will descend to the ground with strong winds.

 

 

 

cirrus

—formed of ice crystals moving very quickly through the atmosphere, occurring at temperatures around –40°C to –60°C, does not produce precipitation 6 to 12 km altitude

Shape  of white filaments, like feathers or commas, with a fibrous aspect and/or a silky shine. Very thin and transparent, they let the sun pass through, even if they dull its shine. They are essentially composed of small scattered ice crystals. They appear in the sky before other clouds that will cause a disturbance

Effect They are a sign of good weather and their precipitation never reaches the ground. If followed by Cirrostratus, they often precede a disturbance.