Look at these mammatus clouds I found while out today. These appeared on the underneath side of the anvil top of the storm that rolled from Terre Haute to Greencastle Wednesday afternoon. Individual pouches of mammatus clouds can range in diameter of 1 to 3 kilometers, if you can imagine that. They are created by the downdrafts and updrafts from particularly severe thunderstorms, such as the ones we've seen across central Indiana in the last week.