Activity | Cloud Spotting
A cloud is simply a large group of tiny water droplets that we can see in the air. But they come in all sorts of shapes and sizes, can tell us what the weather will be like and play a fundamental role in the workings of our planet.
Learning to identify different cloud types not only makes you look pretty clever but can help you forecast what conditions you might face on your day's adventuring.
Low clouds (base usually below 6,500 ft)
Stratocumulus is the most common type of cloud on the planet and is quite variable in its appearance. Generally it is a low, white or grey cloud that has a definite structure. Stratocumulus cloud can be continuous or in broken sections, but the base always looks textured.
Cumulus clouds are some of the easiest clouds to identify. They look like fluffy white sheep or cotton wool balls floating in an otherwise clear blue sky. They tend to form between 1,500 and 5,000 ft and in this form are associated with fine weather. As cumulus clouds gain more vertical development they tend to look a bit more bushy or bubbly at the top – some say like a cauliflower – and cumulus with sufficient depth can deliver a rain shower.
Stratus is low, featureless water-droplet cloud. It doesn’t have the structure of stratocumulus. Stratus can be in continuous sheets or broken into raggedy patches.
Cumulonimbus clouds form from cumulus clouds as the vertical development continues from a base of around 2,000 to 3,000 ft up to altitudes of around 30,000 ft. Cumulonimbus clouds are ‘thunder clouds’. These can produce heavy rain, hail and thunderstorms. If you can look at cumulonimbus from a distance you will see a strong vertical development with a top that looks like a blacksmith’s anvil – flat and spread out. The tops will also look fibrous, where ice crystals are forming. If you are directly underneath cumulonimbus it can seem very dark because there’s a lot of cloud above you, cutting out sunlight. This can be accompanied by heavy rain and squally winds as well as thunder and lightning.
Mid level clouds (base usually between 6,500 and 20,000 ft)
Altocumulus looks as though it’s made up of individual blobs. Like stratocumulus it has a definite texture. The difference is the altitude – typically 8,000 to 18,000ft. Altocumulus can range from being patchy to forming a more extensive layer.
Altostratus is a thin, featureless uniform layer of cloud, often in large sheets. When you can see the sun or moon through thin altostratus, it may appear to have a halo or glow around it. When ice crystals form in the cloud, the sun or moon can look like it’s being viewed through frosted glass. Around sunset or sunrise, when the underside of the cloud is illuminated, the altostratus may look like it has more patterning, but nothing as textured as altocumulus.
Nimbostratus is another featureless cloud type. It is thicker than altostratus and its base tends to drop lower and bring with it persistent rain, sleet or snow. Nimbostratus can have more raggedy clouds underneath it. You won’t be able to see the sun or moon through nimbostratus.
High clouds (base usually at 20,000 ft or above)
A uniform layer of thin, grey cloud at great height. You can still see the sun or moon through it and because the cloud contains ice crystals, these bright objects can appear to have a ring around them.
Cirrus clouds form from 18,000 to 30,000 ft and look wispy or like horses’ tails caught in the breeze.
A collection of blob-shaped clouds, very high. You don’t see these often but when you do they look very pretty at sunset.
Sometimes the atmosphere behaves in such a way as to create particular species of clouds with distinctive or unusual features. One example is lenticular clouds. Excitingly, these can look like flying saucers. Their name actually comes from their shape being like a lens. They are a species of altocumulus cloud that form in standing waves of airflow.
How clouds form
The warmth of the sun evaporates water from bodies of water such as seas and lakes, as well as the land. Warm air can hold more moisture than cold air. When water in the air condenses, it forms droplets, which coagulate to form clouds.
Condensation in the atmosphere happens for two main reasons – the air picks up so much water through evaporation that it becomes saturated, or the air has cooled and can no longer hold as much water.
Forced cooling happens locally when warmer air near the ground is pushed higher into colder air above or, on a larger scale, when warmer air from hot parts of the planet collide with colder air from cool regions.
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