Mammatus Clouds - "True to their ominous appearance, mammatus clouds are often harbingers of a coming storm or other extreme weather system. Typically composed primarily of ice, they can extend for hundreds of miles in each direction."
The Cordón Caulle volcano in central Chile is pictured in all it's glory by Chilean photographer Francisco Negroni. His stunning snaps show forks of volcanic lightning to create an incredible light show.
Weather pictures of the year 2011: lightning, auroras, snow and ice
Extreme weather events, such as these multiple tornadoes, are more likely as a result of climate change. See more: http://news.nationalgeographic.com/news/2013/13/130215-severe-storm-climate-change-weather-science/