Cloud Spotting for Beginners Part 1: Altocumulus

Welcome to the first part of our cloud spotting for beginners series! A series where we guide you through the most common clouds in the sky.

The Altocumulus is most typically a layer of individual or conjoined cloud clumps that are known as ‘cloudlets’.

One of the ten cloud genera, it is the mid-level equivalent of the lower Stratocumulus and higher Cirrocumulus equivalents, forming between 2,000 and 7,000 m (6,500 and 23,000 ft in mid-latitude regions of the world.

Of these three main cloud types, Altocumulus tends to be the most dramatic. Its cloudlets can appear arranged in strikingly regular patterns, like countless buns laid out on a baking tray, and they can extend right across the whole sky.

By contrast, the lower Stratocumulus tend to look scrappier, their forms churned up by the interactions of the winds with terrain and thermals, and the higher

Cirrocumulus tend not to extend over so much of the sky, their tiny cloudlets arranged across in patches.

How are Altocumulus clouds formed?

Some regular patterns of Altocumulus result from ‘convection cells’. Whenever a broad layer of warm, moist air develops beneath a layer that is distinctly cooler, the more buoyant air beneath wants to float upwards.

It can’t all float up at the same time, since the cooler air needs to sink down to replace it, and so the movement naturally arranges itself into rising pockets of warmer air with regions of sinking cooler air in between.

The cloudlets of Altocumulus form where the air rises and the gaps that can separate them appear where it sinks.

Of all the cloud genera, Altocumulus make for the best sunrises and sunsets. Lit from beneath by the warm hues of a low sun, its bun-like cloudlets appear for a few glorious moments golden and baked to perfection.

Keep your eye out for the rest of our Cloud Spotting series and don’t forget to submit your weather and climate photos to the Standard Chartered Weather Photographer of the Year Competition by 18 June. Submit your photos via the Zealous submission platform to be in with a chance of winning up to £5,000!

Submit your photo to Standard Chartered Weather Photographer of the Year

This post is an excerpt from the RMetS book Weather A-Z. The original author is Gavin Petor-Pinney, Founder of the Cloud Appreciation Society, who wrote a portion of the book on the clouds that capture his imagination. Photo © Steve Carr.