These thunderheads are brewing over the midwestern United States, a region where thunderstorms can whip up pretty damn fast. Courtesy of NASA, this image is one of a series running on the Boston Globe's website to celebrate the work done by the International Space Station. Want to see what this kind of cloud looks like a little closer?
This image is of a cumulonimbus cloud over Africa. It has a similar shape to that of the thunderhead, though it doesn't necessarily have to cause thunderstorms. Often it will, however.
You can see a ton of other images in this series at the Boston Globe.
The Sky, From Above [Boston Globe]