This is the Mother of all Thunderstorms. The 'Mothership'! This is the winning photo taken by Marko Korošec in eastern Colorado on May 28, 2013. It won the first place in the 2014 National Geographic Traveler Magazine Photo Contest, without any doubt.

Take a close look at it here. It really does look like aliens or unspoken horrors about to descend on us.

Here's Korošec describing the photo:

While on storm chasing expeditions in Tornado Alley in the U.S. I have encountered many photogenic supercell storms. This photograph was taken while we were approaching a storm near Julesburg, Colorado, on May 28, 2013. The storm was tornado warned for more than one hour, but it stayed an LP [low precipitation] storm through all its cycles and never produced a tornado, just occasional brief funnels, large hail, and some rain.

There's an alien hiding inside that supercell. We're sure of it.