A type of rare and tube-shaped cloud formation created by a cold front ploughing under the warm, moist air that's closer to the ground. Roll clouds belong to a family of low-forming clouds known as arcus clouds and are related to the more common, wedge-shaped shelf cloud. Roll clouds are sometimes born out of a thunderstorm's gust front, and they are rolled into shape by storm winds. But unlike shelf clouds, rolls clouds are not attached to the rest of a storm or any other cloud formation.