# Clouds

**URL:** <https://boards.straightdope.com/t/clouds/19495>\
**Category:** Factual Questions\
**Created:** [May 14, 2000, 8:50am UTC](https://boards.straightdope.com/t/clouds/19495 "2000-05-14T08:50:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\
**Post date:** [May 14, 2000, 8:50am UTC](https://boards.straightdope.com/t/clouds/19495/1 "2000-05-14T08:50:06Z")

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I know, or at least think I know, what clouds are. A bunch of very small water droplets. But I don’t understand why they seem to have a definite “floor” or why they don’t simply disperse like smoke. How can you have a few discrete clouds just sitting in an otherwise cloudless sky?  
What sets their altitudes?

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**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\
**Post date:** [May 14, 2000, 9:12am UTC](https://boards.straightdope.com/t/clouds/19495/2 "2000-05-14T09:12:54Z")

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Air pressure, above or below a certain point they might condense or be evenly spread across the sky.

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**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\
**Post date:** [May 14, 2000, 4:56pm UTC](https://boards.straightdope.com/t/clouds/19495/3 "2000-05-14T16:56:28Z")

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It’s temperature. There is just about as much water (in the form of vapor) below the cloud, but it’s warm enough there that it doesn’t condense. Above a certain point, it’s cool enough to condense and droplets are formed. As to why clouds have tops, I suppose the air is just too dry beyond a certain point. Humidity drops off very quickly with altitude.

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**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\
**Post date:** [May 14, 2000, 4:56pm UTC](https://boards.straightdope.com/t/clouds/19495/4 "2000-05-14T16:56:33Z")

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For a pretty good overview, try:  
[http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/home.rxml](http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/home.rxml)  
Follow the pages beginning with **Development** and then cross-check it with **Cloud Types**. The info is s[read pout over quite a few pages, but it loads very quickly and each page has specific information. Actual cloud boundary development is described beginning about four pages into **Development**.

(I think this is the replacement site for the old COVICS site, although they don’t have a direct mention of that fact.)