A Morning Glory cloud is a roll cloud, or arcus cloud, that can be up to 1,000 kilometres (620 mi) long, 1 to 2 kilometres (0.62 to 1.24 mi) high, often only 100 to 200 metres (330 to 660 ft) above the ground. The cloud often travels at the rate of 10 to 20 metres per second. Sometimes there is only one cloud, sometimes there are up to ten consecutive roll clouds.

They have been called “the biggest waves on the planet”. The wave may occur without the appearance of any clouds.

The local Garrwa Aboriginal people called it kangólgi. Royal Australian Air Force pilots first reported this phenomenon in 1942.