Roll cloud visible in the area on Tuesday morning

Some morning commuters caught a look at a rare tube-shaped cloud rolling across the sky on Tuesday morning, and it wasn't a tornado. This horizontal spinning tube of clouds is called a roll cloud.

Roll clouds and shelf clouds are the two main types of arcus clouds, which appear along the leading edge of thunderstorms or gust fronts. Roll clouds are rarer, making them a striking sight.

Shelf clouds are more common and are attached to the base of thunderstorms, while roll clouds are detached and twirl on their own. Both form when forward-moving pools of cold air undercut and lift the warm air ahead.

A cold front that moved through the area on Tuesday morning caused the roll cloud to develop from Kansas through Mid-Missouri. These clouds are not a sign of severe weather, but their rarity can make them appear more ominous.

When you see a shelf cloud attached to a thunderstorm, that's the time to head inside. Shelf clouds signal a strong downdraft pushing out of the storm, and you can expect strong winds and heavy rain to follow quickly.

Some parts of the world see roll clouds more frequently because of their unique geography. Queensland, Australia, predictably sees roll clouds form on fall mornings over the Gulf of Carpentaria