Cumulus clouds, distinguished by their puffy appearance, form from the condensation of water vapor in areas where convection occurs. As parcels of air are heated, they rise because of buoyancy. As the air rises, it becomes cooler. When the air reaches the dewpoint, water vapor condenses into droplets, which form a cloud. The condensation of the water vapor, however, causes the air to become warmer; if atmospheric conditions are unstable, cumulus clouds may attain great vertical development. The base of a cumulus cloud is typically well below 8000 feet above sea level, but the height of the top of cumulus a cloud may vary greatly. The larger or taller a cumulus cloud, the more likely it is to produce precipitation or to develop into a cumulonimbus cloud, which may produce a thunderstorm or severe weather.