CHARLOTTE, NC (WBTV) - See the attached picture. Thunderstorms, as you might imagine, are big, towering clouds. It's not unusual for a thunderstorm to push 50,000 feet up into the atmosphere. That's 10 miles high!
As it pushes upward into the higher levels of the atmosphere, the updraft in the cloud (sometimes reaching 100mph straight up) actually bumps the layer of air above the storm up and over it. The layer of air flowing over the top if it, behaves much like water does flowing over a rock in a stream.
As the layer of air flows over the top of the cloud, if the layer is close to saturation, the rising motion of that air cools the layer just enough to cause condensation (in this case ice crystals) and that's why you see that 'cap' cloud on top, it's actually a small cirrus cloud.
It's also known as a Pileus cloud.
You are seeing the shadow cast by that tall cloud into the upper atmosphere by the setting sun. This is truly an amazing array of atmospheric optics.
Thanks to Amanda Trivette for sharing her picture!