This is an awesome picture. Supercell Thunderstorm by Sean Heavey, nationalgeographic: A supercell thunderstorm rolls across the Montana prairie at sunset. This was a winning shot in the 2010 National Geographic Nature Gallery Photo Contest.
Image by Mike Hollingshead: An amazing supercell tracks across southern Nebraska, producing other-worldy storm structures. At times, this storm looked like a giant tsunami in the sky. The supercell formed after two supercells merged near McCook Nebraska.