Ever heard of The Morning Glory cloud (arcus cloud, commonly referred to as a roll cloud)? Perhaps not, unless you’re way into meteorology, or you fly hang-gliders or sailplanes.
Here’s a pretty good photo of some guy soaring The Morning Glory. When it forms over northern Queensland, Australia, it can stretch for as long as 600 miles, continuous, and a hang-glider or sailplane can soar along its windward side just as if it was a beach cliff or mountain ridge.
Here’s another cool photo of a roll cloud that formed over Missouri this last January. And here’s more info on The Morning Glory.