Rare, menacing roll cloud moves across northern 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. This cloud type is known as a roll cloud or arcus cloud.

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


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.

'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.

These clouds are relatively rare, less common than its cousin the shelf cloud, which often can be found along the leading edge of thunderstorms, forming along their gust fronts. Roll clouds seldom produce violent winds, whereas shelf clouds are sometimes a harbinger of severe weather.

Here is a large assortment of the roll cloud pictures, photographed by readers across northern Virginia this morning.