It is very common for a sunny morning to transition to a partly cloudy afternoon during our warm season. Many afternoons will be dotted with fair-weather cumulus clouds.
An acute observer may notice they form at differing heights on a daily basis. How far above the ground the bottom of a cumulus forms is determined by the surface temperature and dew point. The air temperature will fall approximately 5.5 degrees per 1,000 feet, but the dew point falls at 1 degree per 1,000 feet.
Therefore, the two temperatures approach each other at a rate of 4.5 degrees per 1,000 feet. For example, if it was 90 degrees with a dew point of 75 degrees, a cumulus cloud would form around 3,300 feet, but on that same day if the dew point was 59 degrees the cumulus cloud would form at a height of 7,800 feet.
So the more humid it is, generally speaking, the lower the cumulus clouds form.
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