Pileus Cloud Above Roswell, Georgia
October 18, 2011
This photo shows a developing thunderstorm east of Roswell, Georgia on the evening of August 5, 2011. The towering cumulonimbus is displaying a prominent pileus cloud -- the smoothed form capping the storm cloud. Pileus take shape when a layer of humid air is pushed by updrafts at velocities of 40 ft (about 12 m) per second or greater. If this layer is nearly saturated, the additional lift from below will often completely saturate it. A pileus cloud is an example of an accessory cloud. Photo taken at 8:11 p.m. local time.
Photo details: Canon SX100IS camera; 1/500 sec. exposure; f/4.0; ISO 80.