A lenticular cloud with Kelvin-Helmholtz wave clouds hovers above south France. (Eric Plouvin)

“Qui vivra verra!” He/she who lives, shall see!

French photographer Eric Plouvin looked up to see not one but two rare cloud types in the sky.

This week, we are heading across the pond to southern France, to discuss the science behind this incredible photo. While it seems like a simple, round cloud, it is so much more that. This cloud, boasting both lenticular and Kelvin-Helmoltz formations, was spotted near the Pyrenees mountains, which is exactly where we would expect to see them.

I have written about lenticular clouds and Kelvin-Helmholtz clouds several times in the past, and they have one thing in common: They are most common around mountain ranges. This is because mountains provide the lift, wind shear and associated gravity waves needed to produce these unusual cloud formations.

Lenticular clouds (the UFO cloud): They form in stable environments with strong winds aloft, where moist but stable air flows over a mountain creating standing gravity waves on the downwind (or lee) side. Generally the mountain range must be perpendicular to the prevailing winds. If the air is cool enough to condense, a cloud forms. Is there any wonder these clouds are often mistaken for UFOs? Indeed, the cloud pictured above resembles a flying saucer.

Kelvin-Helmholtz clouds (the wavelike clouds): Known as “billow clouds,” these form in unstable atmospheres with very strong winds and especially when there is wind shear present. Wind shear describes air moving at different speeds and/or directions with altitude. Strong winds aloft exert force on the top of the cloud causing parts of it to collapse or curl forward over mountain peaks. This allows the cloud formation to take on a wavelike appearance. You can see it flanking the upper right side of the lenticular cloud.

So the presence of mountain ranges and strong winds are the two ingredients needed to produce these cloud types, and that is exactly what France has experienced over the past week as western Europe was lashed with strong winds and heavy rain from a series of storms. In fact, the Seine River flowed at an abnormally high level through downtown Paris thanks to rounds of heavy rain.

My favorite part about writing about this photo was seeing how weather is a universal language. I cannot speak French, but when I saw this photo on Twitter I most certainly recognized “lenticularis” and “Kelvin-Helmholtz.” Conversing with the French photographer gave me even more opportunities to immerse myself in the romantic language. Here is what Eric Plouvin had to say about taking the photo, first in French and then the English translation.

Bonjour, merci! Oui j’ai pris la photo dans le sud de la France (à proximité du massif des Albères (pas très loin du Canigou), dans les Pyrénées-Orientales). Et oui bien sur vous pouvez la partager.

Hello, thank you! Yes, I took the picture in the south of France (near the massive Albèra Massif (not far from Canigou), in the Pyrenees-Orientales). And yes of course you can share it.


Weather is awesome. #CWGPicOfTheWeek