The moment a 'horizontal tornado' rolled in over the skies of Virginia

A cloud shaped like a giant rolling pin or sideways tornado had people craning their necks for a better look in Washington DC yesterday.

The unusual weather phenomenon, known as a roll cloud, stretched in a long line low in the sky at about 7.30am.



As it crept across the region, many people snapped pictures of the odd-looking cloud, which they posted to Twitter and Facebook.

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Rolling in: The arcus cloud was spotted hovering over the National Weather Service station

It is such an unusual sight that even meteorologists at the National Weather Service's offices in northern Virginia took a picture of it as it loomed over their offices.



The rare cloud type is caused by changes in air temperature and wind, which roll the cloud into its unusual shape, according to the Washington Post .



Although it may have looked ominous, the formation, also known as an arcus cloud, was a sign of nothing more than a few showers.

' Sinking cold air causes warm, moist air on the planet’s surface to climb to higher altitudes, where the moisture condenses into cloud form,' according to Live Science .

Low: The roll cloud appears close to the ground as it drifts over a road in Dulles

Tube: The rare formation looks like a rolling pin stretching across the sky

'Winds from the storm "roll" the cloud parallel to the horizon, creating an effect that looks much like a horizontal tornado.'

The cloud moved quickly over Virginia and the Washington DC area, with some people reporting gusts of wind as it passed over them.





Looming: The cloud looks more like the crest of a wave as it drifts over this Chantilly neighborhood

Signs: It may look ominous but the cloud formation signifies nothing more than a few showers