Cumulonimbus Cloud Over Africa: High above the African continent, tall, dense cumulonimbus clouds, meaning "column rain"; in Latin, are the result of atmospheric instability.Courtesy NASAGot this image from NASA's "image of the day" feature yesterday. Its beautiful, awe-inspiring. And also, a bit scary that these are the kinds of clouds associated with lightning, high wind speeds and tornadoes - things that can be fun (I love a good harmless thunderstorm) and also devastating. Learn more about cumulonimbus clouds here.