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I'm trying to see if I understand the concepts of saturation, vapor pressure and cloud formation correctly.

When, at a given temperature and height in the atmosphere, the rate of evaporation and condensation are equal, then the air is said to be saturated and clouds form (assuming the presence of nuclei).

If the rate of evaporation is greater than the rate of condensation, a state of undersaturation is reached and no clouds form.

When the rate of evaporation is less than the rate of condensation, a state of supersaturation is reached and clouds form.

Is my understanding of this correct?

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    $\begingroup$ Welcome to ES SE. Before we can help you can you tell us what you have been reading i.e. URLs, ? $\endgroup$
    – user1066
    May 19, 2018 at 10:00
  • $\begingroup$ I've been trying to teach myself atmospheric science from a variety of sources, from textbooks, online lecture notes, and general science books. $\endgroup$
    – Steven
    May 20, 2018 at 1:48
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    $\begingroup$ Might be useful to summarize what books you have been reading specifically the sections which you do not understand $\endgroup$
    – user1066
    May 20, 2018 at 2:36

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The height at which clouds form is called the cloud condensation level (CCL), where air lifted by convection powered by temperature differences cools and condensates. When it comes to basic physics, yes, evaporation would need to be less (i.e. zero) for condensation to occur. However, this is not necessarily the correct way to look at it, as relative humidity is the determining factor for cloud formation. Relative humidity depends on temperature and pressure. As a volume of unsaturated air cools, its relative humidity increases. If sufficiently cooled, the relative humidity becomes 100%, the temperature equals the dew point, and clouds form. So it's less to do with evaporation and condensation than the amount of humidity, and the temperature (and temp gradient) and pressure of an air mass.

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