formation of a convective cloud

How do clouds form?

Clouds are possibly the most interesting (and beautiful) of all weather phenomena. While there are a wide variety of cloud shapes and sizes, they are all made of the same thing: condensed water or ice. The air in the cloud has been cooled (almost always because it is rising) and it can no longer hold all of the water vapor it contains. Some of that (invisible) water vapor condenses to form (visible) cloud droplets or ice crystals.

The cloud example pictured above is considered "convective", because it is produced from warm air pockets rising ("convecting") from the underlying surface. Convective clouds are typically smaller, a hundred yards to a few miles across. "Stratiform" clouds, however, typically cover much larger areas and are caused by much broader layers of more slowly rising air. Stratiform clouds have a more uniform, featureless appearance, and often cover the whole sky. Some different types of clouds can be seen here.
Interesting facts:
DROP SIZE AND CLOUD APEARANCEThe smaller the drops in a cloud the brighter the tops appear (and the darker the bases). Smaller droplets scatter more sunlight, while large drops allow more sunlight to pass through. This explains why the heavily raining part of a shower cloud or thunderstorm is usually brighter than just the cloudy part. The cloud droplets have combined into large raindrops, which allow more sunlight to pass through them.
(page last updated 6/1/2012)
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