Sometimes the sky looks like it is filled with popcorn.
The pieces of popcorn are actually independent heaping cumulus clouds that form on top of a stable air mass between 10,000 and 20,000 feet (3,048 and 6,096 meters) in the air.
Above this layer the atmosphere must be full of moisture and small circular movements of warmer and cooler air rising and sinking to create the mounting puffs of cumulus clouds.
The spaces in between the popcorn pieces are evidence of cool, dry air sinking. The clouds themselves show that the warmer air is rising, cooling, and condensing.