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. Clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules "clump together" faster than they are torn apart by their thermal energy. 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 directly ("convecting") from the underlying surface. Convective clouds are typically smaller, a hundred yards to several miles across. "Stratiform" clouds, in contrast, typically cover much larger areas and are caused by much broader layers of more slowly rising air (see below), often associated with extratropical cyclone activity. Stratiform clouds have a more uniform, featureless appearance, and often cover the whole sky. This info was gathered from wikipedia at http://www.weatherquestions.com/How_do_clouds_form.htm