Category: Cloud of the Month

Every month, we choose one of our favourite photographs from the Cloud Gallery to become our Cloud of the Month.

June 2024

The illusion of perspective is at its most impressive when you observe beams of light and shade, known as anti-crepuscular rays, from the window of an aircraft. That’s why we featured some as Cloud of the Month for June…

May 2024

Only one of the ten main types of cloud can produce lightning. Only Cumulonimbus has the superpower to shoot electricity through the air, which is why we’re featuring it as Cloud of the Month for May…

April 2024

Fluctus is a cloud formed by a particular wind pattern known as wind shear. With its breaking-wave curls, it is the most iconic of all the wave clouds, and it features as Cloud of the Month for April…

March 2024

It’s this season’s ultimate in mountain fashion. Check out the cap cloud, which we feature as Cloud of the Month for March…

February 2024

Ever wondered how low a low cloud can go? In Cloud of the Month for February, we introduce you to the blanket of cloud that can form right down at the ground and fill mountain valleys to the brim…

January 2024

Last month saw the most dramatic display over Europe in over 15 years of the most colourful cloud in our skies. We explain all in Cloud of the Month for January…

October 2023

Cirrocumulus usually appears in patches that don’t hang around for long. October’s Cloud of the Month shows an unusually rare expansive form of this fleeting cloud…

August 2023

On a hot, still day in the height of summer, a spinning cloud of dust can develop. It’s known as a dust devil, and it features as a very dry Cloud of the Month for August…

July 2023

A cavum, or fallstreak hole, is the perfect cloud feature for any clouspotter with a sweet tooth, as we explain in Cloud of the Month for July…

June 2023

In Cloud of the Month for June, we introduce the murus cloud, which appears beneath huge storm systems and likes to give birth to tornadoes…

January 2023

This form of Altocumulus cloud, spotted over Winsted, Connecticut, US by Pamela Crimmins (Member 48,931), reveals how the winds in our lower atmosphere can flow in different directions at different levels. We explain why in Cloud of the Month for January…

December 2022

When you wake on a clear, freezing morning to sparkles in the sunlight and a host of bright arcs, rings and spots in the sky, you can thank the subtle ice fog known as diamond dust. This glittering morning mist plays the starring role in Cloud of the Month for December…

November 2022

Meet the cloud formation that resembles those traffic safety markings on roads. We introduce Stratocumulus undulatus in Cloud of the Month for November…

Cloud of the Month, Oct 2022

October 2022

Meet the two ghostly optical effects caused by clouds: the fogbow and the Brocken Spectre, which both feature in Cloud of the Month for October…

July 2022

Building storm clouds can sometimes wear delicate cloud hats. And they generally go on to eat their hats. We explain all in the Cloud of the Month for July…

June 2022

A sky festooned with dramatic lobes of cloud, known as mamma, is often a sign that storms are passing. We explain all in Cloud of the Month for June…

Cloud of the Month for May 2022

May 2022

Ever wondered why clouds sometimes arrange themselves into regular patterns of tiny cotton balls? We explain what causes this with a demo you can perform in your own kitchen with a panini toaster in May’s Cloud of the Month.

April 2022

They say every cloud has a silver lining, but some have multi-coloured ones too. That’s when the edges of a cloud are embellished with delicate pastel colours known as cloud iridescence…

March 2022

The Eyebrow Cloud That’s Waiting to be Made Official

This cloud formation should have a Latin name, but it is yet to be classed as an official cloud type. It can appear in the turbulent airflows downwind of mountain peaks, and we think it looks like eyebrows in the sky.

This would be a good cloud to be added to the list of types because it has a distinctive appearance that’s easily differentiated from other formations. Also, pilots would likely want it to have a name for practical reasons: so that they can learn to stay well away from it. This cloud reveals where turbulence in the mountain airflow is particularly chaotic and violent, which is where no glider pilot wants to fly.

The turbulence develops as part of the rising and dipping flow of air as winds pass over mountains. Much of the airflow is smooth, rising to pass over the peak and dipping back down again beyond, like water flowing over a rock in a stream. But just as the water flowing in a stream can break and foam at a particular point beyond the obstacle, so can the wave of the airflow break at a particular point downwind of the mountain peak. Where this happens, if it does, depends on the shape of the terrain and the speed of the wind. Often the breaking wave of air is invisible. Sometimes, it produces a churning, roll-like cloud described by pilots as a rotor cloud. Sometimes, when the air tumbles over itself, it makes the distinctive shape of eyebrow clouds.

We’ve had examples of this unnamed formation sent in by members from around the world, including examples over the Sierra Nevada of California, US, the mighty Himalayas of Nepal, and the alpine peaks of Switzerland like The Eiger mountain and The Jungfrau. We even have a Latin name in mind for it. This was suggested to us by Latin scholar Rick LaFleur, Franklin Professor of Classics Emeritus at the University of Georgia, US when we asked him how the Romans would have referred to an eyebrow. Rick suggested the term supercilium, which is Latin for ‘eyebrow’.

It’s been a few years since the Cloud Appreciation Society last argued that the official naming system for clouds should have a new classification of cloud added to it. The chaotic, wavy-looking asperitas cloud was eventually accepted as a new cloud type by the World Meteorological Organisation (WMO) after we’d argued the case for it to be given a name. Asperitas was added to the WMO’s official reference work The International Cloud Atlas back in March 2017. That was exactly five years ago this month. Perhaps it’s time to start a new cloud-classification campaign and raise some eyebrows with the supercilium cloud?

Altocumulus ‘supercilium’ spotted by app user ‘Cielo’ over the Sangre de Cristo Mountains of New Mexico, US.

December 2021

When Claudio Cattaneo (Member 13,236) took to the ski slopes of Crans-Montana, Switzerland early on a cold December morning, he was greeted by a glittering display of halo phenomena…