RECAP
Arcus clouds: low, horizontal cloud formations below the thunderstorm’s rain-free base. The name ‘arcus’ comes from the latin word for ‘arch’. There are two types of arcus clouds: shelf cloud and roll cloud.
Shelf cloud: a shelf cloud is a common type of arcus clouds. It is a low, wedge-shaped, horizontal arcus cloud, attached to the base of the thunderstorm.
Whale’s mouth:
Roll cloud:
