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.
Lenticular Cloud over Klyuchevskaya Sopka Mountain, Russia by Denis Budkov: Klyuchevskaya Sopka is a stratovolcano, the highest active volcano of Eurasia. Its steep, symmetrical cone towers about 100 kilometres from the Bering Sea.