 A shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm cumulonimbus, but could form on any type of convective clouds.Rising cloud motion can often be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent and wind-torn.Cool, sinking air from a storm cloud's downdraft spreads out across the land surface, with the leading edge called a gust front.