Extraordinary Mountain Clouds Part 2: Mont Blanc’s Hat

The Mont Blanc will be the center piece of your Tour du Mont Blanc, or your starting point if you hike the Chamonix to Zermatt Haute Route. It reaches as high as 4810 meters up into the sky, making it the highest mountain of the Alps, and even of Europe. And like all high mountains, Mont Blanc creates its own clouds (see previous blog: Extraordinary Mountain Clouds). Its most striking cloud has a very characteristic shape: it harmoniously mimics the shape of the mountaintop, covering the summit as if Mont Blanc is wearing a hat.

How the cloud is formed

In technical terms, this lens shaped appearance is called altocumulus lenticularis and its formed by a strong wind that blows over the Alpine giant and descends at the back of the mountain. The cloud becomes visible as soon as the air cools down near the summit and becomes saturated with water vapor. The cloud dissolves again when, at the back of the mountain, the air drops again causing the air to warm up.

For hours

Sometimes Mont Blanc will wear its hat for hours in a row. Although the lens cloud seems to be stationary in the same place, the air creating the cloud continues to flow; as long as the wind continuously blows from the same direction at the same speed and with the same amount of moisture, the cloud will stay visible in exactly the same spot.

Mont Blanc
Mont Blanc is wearing its hat. In technical terms, this lens shaped appearance is called altocumulus lenticularis.

Bad weather is coming!

The characteristic lens cloud is not only well known because of its beauty, but also because it’s letting you know a disturbance is on its way. When Mont Blanc is wearing its hat, the weather will most likely change. This is especially the case when the base of the “hat” is very low, keeping the summit completely out of sight. So, if you see this beautiful cloud above Mont Blanc, you better get your rain gear ready!

Simone van Velzen

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