How does a cloud just disappear from the sky without it raining or wind blowing it away?


So there was [this post]( in r/all of a 5 minute timelapse showing a cloud literally disappear. How does this happen? Was there just a suddenly dry wind? Does this happen often?

In: 2

Clouds aren’t solid objects, they’re made of water droplets. We can see the droplets but not the water in gaseous form around them.

Take the example of a mountain range where the wind pushes moist air up the slopes. As the air cools (due to its expansion at increasing altitude) water vapor condenses and forms these droplets (exactly like on a cold beer glass) and you have a cloud on top of the range.

But does the wind stop there? No, it drags the cloud downslope and the reverse happens: the air heats up and the droplets evaporate, that part of the cloud disappears.

What seems like a permanent structure – “a cloud” – is in fact constantly created (upslope) and destroyed (downslope).

Does this happen often? All the time. I like to take cloud pictures but all too often just going to grab my camera is enough for an interesting cloud to slim down to tatters. We just usually don’t pay much attention.

I can’t say what exactly happens in that video, just that the air pocket holding the cloud got somehow heated up.

Clouds are also just the places in the sky where the water droplets are above a certain size (above that size, [Mie scattering]( happens, and you see the droplets as opaque; below it, it doesn’t) . If that water spreads out (by contact with dryer air, for example), the average droplet size will fall, and you’ll stop being able to see them. It doesn’t necessarily mean that the water has somehow vanished.

Edit: Realised I’d misspelled “Mie”

The same way that the “steam” from your kettle evaporates into the surrounding air.

Clouds are just water vapour, the same as the “steam” from your kettle (steam and water vapour are technically different things). It’s just droplets of water. If the air around it allows it to dissipate, it’ll turn to smaller, more spread out droplets that are basically invisible.

Clouds are visible mainly because winds “push” the water vapour together and keep them together in a rough volume, but the edges are changing and moving all the time, in all 3 dimensions, it’s only kept together by air above, below and sideways keeping it pushed “together”.

When that push becomes uneven, the cloud will spread out and “disappear”, and those same droplets will either float around or fall down or may even be “pushed” to form a new cloud elsewhere later on.