What a beautiful picture taken by 40/29 storm chaser Brian Emfinger, but what is it? It's a Pileus cloud, which is Latin for "skull cap". These clouds are made of ice crystals high atop the troposphere. Thunderstorms have rising air currents that feed the storm's growth. Sometimes these currents take moisture above the tower where it cools and condenses. The lifted layer of air isn't as moist as in the lower levels, so they don't take on much of a vertical growth. Look for them in a moisture rich environment.