Clouds come in a variety of shapes and sizes depending on how and where they formed. Although there are just three main types of cloud, these types can combine to produce other types, each with its own characteristics. In all there are about ten different sorts of cloud, and these are usually identified according to their shape and how high they are in the sky.
Cirrus is usually the highest cloud of all. Here the air is so cold that they are made entirely of ice crystals. Strong winds blow them into streaks across the sky and they are a sign of unsettled weather. Cirrostratus – all high clouds start with the word ‘cirro’. These clouds occur when cirrus clouds spread into a thin, milky sheet. These are again made of ice crystals and the sun usually appears very bright through cirrostratus clouds. Cirrocumulus – these are tiny, high balls of icy, shadow less cloud. They often form in regular waves and ripples and are known as “mackerel sky” because they look like the scales of a mackerel.
Altostratus – medium-height clouds start with the word “alto”. Altostratus clouds consist of water droplets and appear as high, thin layers of cloud. Sometimes a colourful ring appears around the sun in altostratus clouds. Altocumulus – these are medium-height cumulus clouds that look like squashed lines of cotton wool balls. They are similar to the higher cirrocumulus, but are larger and have dark, shadowy sides. They look like fleecy clouds and are a sign that unsettled weather is on the way.
Cumulus – these fluffy clouds are the easiest to spot. They are low-level clouds that usually indicate fair weather. Sometimes, however, they group together during the day and become rain clouds. Cumulonimbus – these are bigger and darker than cumulus clouds and often have flat tops like a blacksmith’s anvil. Nimbus means “rain” in Latin and these towering clouds usually bring rain, hail and even thunder. Cumulonimbus clouds are a mixture of ice crystals and water and can sometimes even be taller than Mount Everest.
Stratocumulus – these are also medium-height clouds and look like long rolls of cloud. They form when cumulus clouds rise and spread out sideways in layers. These clouds can often be seen from an aeroplane, where they appear as an undulating blanket of cloud, with the ground being visible only through narrow breaks. Stratus – are low-level clouds that look like a grey blanket. The thick layers hang close to the ground and may give a damp drizzle, but no real rain. Sometimes the sun shines through these clouds, looking like a silver disc. Higher up, on hills or even from tall buildings, stratus clouds appear as fog.
Nimbostratus – are thick layers of cloud. They start near the ground and nimbostratus cloud can be very tall, often bringing hours of rain or snow.