Roll Cloud Spotted in Texas: 'Horizontal Tornado' Wind Formation Rare, Not Dangerous (Video)

When residents of Armarillo, Tex., peaked outside their windows right before sunrise last week, they might have been a bit surprised. Of course, the forecast may have noted cloudy conditions, but it certainly didn't prepare them for this peculiar picture: a long, tube-shaped formation called a roll cloud running through the sky.

Thanks to truck driver Bonnie Mask, who lives near the area and whose husband, Todd, had the day off, the couple were able to capture video footage of the environmental mystery via their deck in Timbercreek Canyon.

"Apparently, it's pretty rare," Mask said, according to Yahoo News, adding that she had never seen anything like it before. "There was some cool air that blew over as the cloud blew over the house."

Roll clouds are rather rare-a type of arcus cloud that is a category of low cloud formations. Their closely related to shelf clouds-a group of clouds you might see during a thunderstorm.

However, as roll clouds are originally made up of cold air that turn warm and moist via the surface of higher altitudes, this forms the condensed shape of the cloud.

LiveScience notes that winds from a previous storm help the body of air "roll" the cloud parallel to the horizon and create the effect of a horizontal tornado. Fortunately, unlike tornadoes, these clouds aren't dangerous.

So if you happen to see one, count yourself lucky. They're quite the sight and pretty safe.

Want to see this cloud in action? Check out this video, courtesy of YouTube.