Weather watchers in Washington, Virginia, got something of a surprise this morning when a rare 'horizontal tornado' passed over the skies.
The US National Weather Service uploaded a picture of the roll cloud to its Facebook page and wrote: "An outflow boundary from the showers associated with the cold front produced a very well defined roll cloud that passed over our forecast office this morning just before 7:30 am.
"Here's a picture of it as it approached (moving toward the camera)... it was moving very fast! Did anyone else get to see this?"
Hundreds of people commented, with one user writing: "Way cool photo!"
According to The Sun, the cloud is caused when cool and warm air fronts meet and are rolled into shape by winds.
Although they can be associated with thunderstorms, the Huffington Post reports that NASA says roll clouds are not thought to be able to turn into tornadoes.
'UFO cloud's spotted over Aberdeen in Scotland
Amazing pics: 'Tsunami' wave clouds hit Florida coast