An arcus cloud is a low, horizontal cloud formation, usually appearing as an accessory cloud to a cumulonimbus. Roll clouds and shelf clouds are the two main types of arcus clouds.

What do arcus clouds mean?

Arcus clouds are low-level, wide ranging clouds typically associated with powerful storm clouds and thunderstorms. Height of base: Up to 6500 ft. ... Latin: Arcus = Arch. Precipitation: None directly, but heavy showers in the vicinity from cumulonimbus clouds.

Where do arcus clouds occur?

Shelf clouds, also known as arcus clouds, occur at the leading edge of thunderstorms. They announce the arrival of storms and, when combined with cumulonimbus thunderheads, can look like giant alien motherships. Shelf clouds form when the cooler air of a thunderstorm encounters warm, humid air and lifts it.