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9 scary images of shelf clouds

Oct. 5, 2011, 9:02 a.m.
Shelf cloud over Warsaw, Poland

Photo: Dariusz Wierzbicki/Wikimedia Commons

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Warsaw, Poland

This dramatic shelf cloud, seen over Poland's capital on July 5, 2009, certainly looks menacing. It's easy to see why shelf clouds are often confused with wall clouds (drooping formations that can spout tornadoes), but the two aren't as similar as they might seem.

While shelf clouds are capable of causing trouble, they mainly serve as harbingers of more severe weather on the way — and even then, they've been known to exaggerate the threat. Wall clouds, on the other hand, typically form near a thunderstorm's more turbulent backside, as do most tornadoes, and are more likely to cause damage on the ground.