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.

10 thoughts on “March 2022”

  1. I’m glad the name works for you, Sara.

  2. David Worth avatar David Worth says:

    It’s a wonderful formation and reminds me of the delicate caul or lace fat used as a wrapper in cooking. A name based on this could be from the Latin for caul – caput galeatus or caelum (sky) galeatus. But superciliaris sounds good to me.

  3. Steve Clarke avatar Steve Clarke says:

    I like superciliaris but isn’t it a mix of altocumulus (possibly with a bit of lenticularis) that has elements of Fractus and maybe Lacunosus?

  4. George Preoteasa avatar George Preoteasa says:

    Go for it, Gavin!

  5. Kwong Hung Tam avatar Kwong Hung says:

    Awaiting CAS’s proposal since January 2020 when I first saw these eyebrow-like clouds in Hong Kong. Even without high mountains, the small hills in Hong Kong are sufficient to produce turbulence clouds like these.

  6. The other day, here in SW Florida, I saw similar clouds. I’ll be posting them on the ID Clouds forum later to see if they’re the same.

  7. Darlisa Black avatar Darlisa says:

    Superciliaris clouds, perfect! I often see them trailing from the base of a building Mountain wave cloud near the mountain. In fact I saw some today.

  8. Sharon Cox avatar Sharon Cox says:

    This is so amazing. I am a new member and learning. I wrote a short piece for a magazine I edit on clouds but think it’s probably too long to put in here. However – I named my own cloud – the eyebrow cloud. What a coincidence. Though they are slightly different I think, in being lower level. I can’t work out how to upload the image.

  9. Phoebe Ashdown avatar Phoebe Ashdown says:


  10. Sara Fuge avatar Sara says:

    I love these clouds – they are so ethereal and beautiful. I have seen them before over Bodmin Moor in Cornwall UK. I always wanted to have a distinct name for them.

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