When a building Cumulonimbus storm cloud, the tallest of the ten main cloud types, has yet to spread at the top into fluffy edges, often extending in a broad canopy, it is known as a Cumulonimbus calvus. This one, spotted by Miles Roberts (Member 54,531) over South Luangwa National Park, Zambia, has yet to reach up to the tropopause. That’s the boundary between the troposphere and the stratosphere, where the temperature gradient acts like a lid on cloud growth. Once this cloud does reach the invisible temperature lid of the tropopause, it will start to spread out sideways at the top. Miles noticed an African Fish Eagle also looking at the evening’s big Cumulonimbus calvus sky. ‘In the disappearing light,’ he said, ‘it was tempting to imagine the eagle contemplating the remains of the day, settling down for the evening on a favorite snag after a long day fishing in its lagoon.’