Unless you live near the Gulf of Carpentaria, you've probably never seen a cloud like this. It's called a roll cloud and it's both startling and awe-inspiring.
Roll clouds are low, horizontal, tube-shaped clouds that appear to be literally rolling across the sky. It's rare and usually forms in areas where an outflow of cold air meets warmer air. Only certain locations like like coastal California or the Sea of Cortez in Uruguay experience these types of clouds.
The most famous one, the Morning Glory, occurs at the Gulf of Carpentaria. This location has a unique geography that encourages the formation of these clouds. They occur regularly here and have become a tourist attraction for pilots. [Mother Nature Network]
Roll cloud in Racine, WI.
Roll Cloud in Las Olas Beach located in Punta del Este, Uruguay.
Roll cloud in Bowling Green, Kentucky.
Roll Cloud taken from space by the Space Shuttle Atlantis.