An arcus cloud is a low, horizontal cloud formation. Roll clouds and shelf clouds are the two types of arcus clouds.
A roll cloud is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features. Roll clouds usually appear to be “rolling” about a horizontal axis. They are a solitary wave called a soliton, which is a wave that has a single crest and moves without changing speed or shape.
A shelf cloud is usually associated with the leading edge of thunderstorm outflow; roll clouds are usually formed by outflows of cold air from sea breezes or cold fronts in the absence of thunderstorms.
A shelf cloud is a low, horizontal, wedge-shaped arcus cloud. A shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm, but could form on any type of convective clouds.
Amazing Roll Cloud, Tsunami, Tidal Wave looking Cloud rolls over Huntington Beach, CA
Incredible weather phenomenon, known as a “Roll Cloud”, stretched across the the entire length of Orange County, California, USA on April 25, 2012. I shot this video six months ago, (just stumbled across it on my iPhone), in Huntington Beach, CA, and minutes later my friend Carine saw it rolling over Laguna Beach as it made it’s way south. It looked like a giant wave or Tsunami sweeping over from horizon to horizon, similar to the alien ships in the beginning of Independence Day.
Big Roll Cloud at Honeymoon Island Sunset – Dunedin, Florida (iPhone 6 Plus)
Wave Cloud Over Lake Michigan