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The Official MyScience Summer Cloud Guide!

Summer. [CC0]

Clouds in the sky are one of our planet’s most beautiful things and it is pretty hard to imagine a life without them – clouds cover approximately 65% of the earth. The majority of clouds consist mainly of water droplets and ice crystals (something we’ve written about before). Clouds form when moist air rises up and cools down, resulting in the condensation of water. Cloud formation can take place for examples when moisture in the air is rising up on a mountain, or when warmer air passes over colder air.

Sometimes one might think why it seems that clouds are passing by you very fast, while sometimes it looks like they don’t move at all. When clouds seem to pass fast it is likely quite windy, and when they seem to stay stationary the wind is most likely weak. At high heights clouds can move with speed of 100 metres a second or even more!

Generally, clouds can be classified according to their height: low clouds, middle clouds and high clouds. Low clouds are approximately 0-2 km above the ground, middle clouds at an altitude of 2-7 km, and high clouds at 7-10 km. However the border of the cloud height is not that straightforward, because some clouds may stretch vertically. A common example is the Cumulonimbus, maybe better known as the cloud associated with thunderstorms. Why such a weird name for a cloud? Well, cloud classifications is part of science, and in science classification is usually done in Latin.

Cloud Types. Photo: Valentin de Bruyn / Coton [CC BY-SA]

Now when we know how clouds form and why they move at different velocities, we come to the question of why there are so many different kinds of clouds – some look like turtles and some like UFOs. The form of the cloud basically depends on how the wind blows and how the air moves in the vertical direction. Temperature and humidity also affect cloud formation, parameters that vary throughout the atmosphere.

You may have noticed that there are even different colours of clouds – even when the shape is the same. Some are white, while some are grey or blueish-grey, for example. The colour of the cloud depends on how solar radiation – the particles and waves blasted by the sun – reach the cloud. If the cloud is directly under the sun it is most likely white, while if the cloud is in the shadow of a different, higher cloud, it is darker. Even if the cloud is directly under the sun it might look greyish, though, which is the result of high numbers of water droplets in the cloud.

The cute UFO cloud you observed in the sky is actually called a Lenticular cloud. As the name suggests, lenticular clouds are lens-shaped. When moist, stable air flows over a mountain or mountain range, standing waves may occur in the downwind side. The top part of these waves makes for favourable cloud formation conditions, which result in lenticular clouds. When you see these clouds you are safe from dramatical weather changes, as these clouds can only form if the atmosphere is stable.

Leticular Clouds. Photo: Omnisource5 [CC BY-SA]

When you catch cute sheeps in the sky, it means Cumulus clouds. You may be quite without worries, as the risk of rain is once again quite small. But when your cute sheep clouds grow in the vertical direction during forenoon, you might want to do some other activity than outdoor sport during the afternoon, because it is most likely to be rainy.

Cumulus Humilis Clouds. Low chance of rain. Photo: PiccoloNamek [CC BY-SA]

Cumulus Congestus Clouds. High chance of rain. Photo: L-G Nilsson/Skylight

If you observe a mushroom in the sky reaching you, it is better run inside if you don’t want to get wet (or hit by a lightning). When mushroom is spotted in the sky it means that it is already raining under the cloud, and also a thunderstorm may occur. Remember if you are in the middle of an open space when you meet a thunderstorm, try to minimise your surface area and exposure to prevent a lightning to hit you – it may have fatal consequences.

Cumulonimbus Clouds. Run inside! Photo: Griffinstorm [CC BY-SA]

One may find identifying clouds hard in the beginning, but the more you spot them and know, the more fun it is. Here was just a tiny fraction of cloud types and their properties. If you wish to be prepared to all types and shapes of clouds, more information can be found at the World Meteorological Organization’s Cloud Atlas Vol 1 (pdf) and Vol 2 (pdf).

Now when summer has started and the weather is (hopefully) favourable for cloud watching, I recommend everyone to give a shot!

Vilma Kangasaho is a Millennium Youth Camp Alumni studying meteorology at the University of Helsinki. She is interested in climate change and enjoys sports.