a low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.
A low-level, horizontal, wedge-shaped arcus cloud associated with a convective storm gust front (or occasionally a cold front). The shelf cloud is attached to the convective storm's cloud base. Rising motion can be seen in the leading (outer) part of the shelf cloud, while the underside appears turbulent and tattered. Compare roll cloud.