Shelf cloud, Oklahoma, May 7, 2008. A shelf cloud is a low, horizontal, wedge-shaped arcus cloud. A shelf cloud is attached to the base of the parent cloud, which is 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 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. This outflow cuts under warm air being drawn into the storm's updraft. As the lower cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below (wind shear).