Are clouds a solid, liquid, or gas?

I have been looking online and they are often described ambiguously as a "mass". For instance, from NASA:

A cloud is a mass of water drops or ice crystals suspended in the atmosphere. Clouds form when water condenses in the sky. The condensation lets us see the water vapor. There are many different types of clouds. Clouds are an important part of Earth’s weather and climate.

Since they describe it as a vapor, that makes me think it is indeed a gas. But condensation is by definition the change of state from a gas to a liquid. So that makes it sound like it could be a liquid, or contain liquid droplets rather than "freely moving" molecules that typically make up a gas.

But at another web site, which doesn't seem all that authoritative, it says that clouds are a solid, liquid, and gas simultaneously!

A cloud is a liquid, a solid, and a gas.

That does seem intriguing. If I remember correctly, liquids are supposed to be incompressible, and clouds are likely compressible.


The cloud that you see is a mixture of solids and liquids. The liquid is water and the solids are ice, cloud condensation nuclei and ice condensation nuclei (tiny particulates that water and ice condense on). The invisible part of clouds that you cannot see is water vapor and dry air. The majority of the cloud is just plain air in which the invisible water vapor is mixed with and the very tiny water drops and ice particles are suspended in.

A cloud is a mixture of gas, liquid and solids.

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    $\begingroup$ Can I just ask how it's possible to have both liquid water and ice in the same region? If that region has the same temperature and pressure, then water should only be possible in one state, not two. $\endgroup$ – DrZ214 Aug 15 '15 at 22:23
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    $\begingroup$ @DrZ214 0 C is the temperature ice melts and the temperature where liquid water will begin to freeze. It can take quite a while for liquid water to freeze until ice nucleates and freezes a drop. You can do simple experiments to see this (ask a new Q about it). Between 0C and -40C clouds tend to contain both liquid water and ice. Below -40 C outside of vigorous convection they can be pure ice clouds (e.g. cirrus). $\endgroup$ – casey Aug 15 '15 at 23:21
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    $\begingroup$ @DrZ214 For an example of how you can end up with something like that, (which might be entirely unrelated to clouds) read about "supercooled water". youtube.com/watch?v=ph8xusY3GTM $\endgroup$ – Patrick M Aug 15 '15 at 23:27
  • $\begingroup$ @DrZ214 Also see en.wikipedia.org/wiki/Triple_point $\endgroup$ – March Ho Aug 16 '15 at 1:15
  • $\begingroup$ @DrZ214 phys.org/news/2011-11-supercool-doesnt-.html $\endgroup$ – casey Aug 16 '15 at 2:32

A cloud isn't solid any more than a bunch of dust picked up by the wind is solid. It's mostly air, but what you see is tiny suspended particles, so it's no more a liquid than a bunch of dust blowing in the wind is solid. The entire cloud needs another definition because it's so diffuse. Suspended very tiny drops of water or ice crystals is probably the best definition.

If your next question is - how does ice and water not fall to the ground, the answer is that they do fall, but slowly enough that just a 1 or 2 MPH updraft is sufficient to keep a cloud aloft. They fall quite slowly, like the speed of a feather, and it's not hard to keep a feather in the air with a little wind below it.

Finally, water vapor itself is transparent. So clouds aren't water vapor, though they're obviously made primarily from condensed water vapor.

