Roll cloud over Dorset, England

This magnificent acrus cloud, a rare "roll cloud," turned up over Weymouth and Portland in Dorset, England last weekend. Many residents were concerned that the cloud was a tornado. From Dorset Echo (photo by Peter Minster):
Storm.Jpg.Display Met office forecaster Michael Lawrence told the Echo: "It was a roll cloud. It's a relatively rare, low-level, horizontal, tube shaped cloud that's completely detached from the base of a thunder cloud.

"It's most frequently observed on the leading edge of thunderstorms. The cloud rotates about its horizontal axis. They are not tornadoes.

"Rare roll cloud makes its way over Portland and Weymouth" (via Fortean Times)