Known as "kangólgi" to Aboriginal people and "morning glory" clouds to local anglophiles, they most often form in the morning, especially from September to November. Their exact origins are hazy, though, since they aren't associated with thunderstorms like many other roll clouds are.
For starters, roll clouds are generally harmless. While a tornado's vertical vortex can wreak havoc on the ground — destroying entire cities in extreme cases — roll clouds tumble along slowly and horizontally. They also form at the front of thunderstorms instead of the back, where most twisters are born, and they aren't even attached to the storms that spawned them.
