I have the perfect seat for undertaking my lessons on cloud classification. Straight out the back end of our studio I have a panoramic view of the sky and here on the Cambridgeshire Fens the clouds roll through much like they do at sea. It’s usually makes better watching than the TV.
The Civil Aviation Authority and the Met Office appear to agree that there are ten types of cloud, plus a couple of bonus ones. I have been learning the two-letter codes for each of the ten cloud types and practising identifying them.
Clouds can be classified in terms of either their height or their form. The three heights are high (15,000′ to 30,000′), middle(6,000-15,000′) and low(below 6,000′). And the four forms of cloud are cirriform (fairy floss), cumuloform (cotton wool), stratiform(blanket) & nimbus (rain).
There are three high level clouds with a height between 15,000 and 30,000 feet to learn.
Ci – Cirrus clouds are whispy, silky, ghosty clouds high in the sky. Because they are so high in the sky they are made of ice crystals so tend to look very white. The height is high and the form is cirriform.
Cs – CirroStatus clouds are very high hazy, flat featureless blanket. The sun is usually visible through the film as a disk with a red fringed halo. The height is high and the form is stratiform.
There are two middle level clouds between 6,000 and 15,000 feet to learn.
Ac – Altocumulus clouds are like sheets of cotton wool balls fairly high in the sky. They tend to run in lines or waves. The globs may be separated or touching. The height is medium and the form is cumuliform.
As – Altostratus clouds are uniform blanket of greyish or bluish sheet, very slightly transparent usually enough to see the sun as a fuzzy bright white disc through. The height is medium and the form is stratiform.
There are 5 low level cloud types below 6,000 feet to learn.
Ns – Nimbostratus clouds appear as a darkish grey blanket covering the whole sky and thick enough to hide the sun. They are rain bearing. It may be a middle or low height cloud and the form is stratiform.
Sc – Stratocumulus clouds are a white or greyish sheet of lumps or rolls. Showery snow or rain may be associated with these clouds. These are what I see out my window today. They are a low level cloud that are cumuliform clouds that have formed into a stratus blanket.
Cu – Cumulus clouds are the glamour cloud and most peoples favourite cloud. They are fluffy heaps sometimes with a greyish base. Typically cauliflower-shaped but your imagination is the only limit. The height is low and the form is cumuliform.
Cb – Cumulonimbus are high towering storm clouds and are a danger to aviation. Lightening, thunderstorms and hail are usually near these clouds. The height of the base of the cloud is low but the tower may extend high and the form is cumuliform.
Lenticular clouds also need to be mentioned.
Lenticular Ac – Lenticular Altocumulus are smooth, individual, almond-shaped clouds that form over mountains. We saw lots of these as we cycled along the Andes in Argentina and know that the are associated with very strong winds.
The cloud example images above are mostly from the Met Office training website so can’t be argued with. Below are some of my own photos that I have tried to classify, so please do to disagree if you think I have classified any of these wrongly.