Thunderstorms produce a lot of weird phenomena, many of which are easy to miss amid the urgency of tornadoes, floods or lightning. But before a storm arrives, and sometimes just out of the blue, rare "roll clouds" command attention as they float overhead.
"It was amazing," photographer Rob Sharrock told the Daily Mail in 2010, after spotting a roll cloud over Warrnambool, Australia. "I just looked up in the sky and said, 'Bloody hell, what on Earth is that?' It seemed to go on for miles."
To see more, and unravel some of the mystery behind these stormy spindles, check out the following gallery of rockin' roll clouds from around the world. (Text: Russell McLendon)