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9 ominous images of roll clouds

Roll clouds in the Gulf of Carpentaria

Photo: Mick Petroff/NASA

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Northern Australia

Roll clouds can occur almost anywhere, but they seem most at home in Australia's Gulf of Carpentaria, reportedly the only place on Earth where they can be reliably predicted.

Known as "kangólgi" to Aboriginal people and "morning glory" clouds to local anglophiles, they most often form in the morning, especially from September to November. Their exact origins are hazy, though, since they aren't associated with thunderstorms like many other roll clouds are.

Morning glory clouds regularly attract glider pilots to the Gulf of Carpentaria — including Mick Petroff, who shot this photo in 2009 near Burketown, Queensland.