By Ron Childers, Chief Meteorologist
MEMPHIS, TN (WMC) -
A couple of weeks ago after a day of storms in the Mid-South, a viewer in Hardin County sent us a picture of a strange formation in the sky.
Some members in our newsroom asked, "Is that a cloud or a UFO?"
Personally, I don't think we're alone in the universe, but that was not the proof we're looking for. That was a photo of a roll cloud - a rare form of arcus cloud.
It's a low, horizontal, tube-shaped cloud formation, a rolling solitary wave.
There are two types of arcus clouds, roll clouds and shelf clouds. Shelf clouds are typically found along the leading edge of a super-cell thunderstorm resulting from the downdraft of the storm.
Roll clouds can sometimes form in advance of the shelf cloud when a horizontal vortex forms. It can then become detached from the structure as the storm decays and continue moving along appearing to be rolling horizontally across the sky.
They are typically found along coastal regions resulting from a sea breeze or cold front. The picture we received was a result of storms that had been moving through the area the day the photo was taken.
As the storms decayed, the downdraft combined with forward movement and gravity to produce the giant roll cloud that moved through Hardin County making for a uniquely beautiful yet, somewhat shocking sight for those who saw it.