Heavenly Billows

Cumulus clouds like these often look like billowing puffs of cotton. The base of the clouds tends to be flat and perhaps just 330 feet (1,000 meters) above the ground with rounded cloud tops, according to the National Center for Atmospheric Research. When the tops of cumulus clouds start to resemble a head of cauliflower, they are called towering cumulus (as shown here); these can grow upward and even develop into thunderstorm clouds called giant cumulonimbus clouds.