A wall cloud (or pedestal cloud) is a large, lowering cloud formation that develops beneath the base of a cumulonimbus cloud that often forms tornadoes. It is typically beneath the rain-free base (RFB) portion of a thunderstorm, and indicates the area of the strongest updraft within a storm. Wall clouds are sometimes an indication of a rotating mesocyclone in a thunderstorm, and most strong tornadoes form from wall clouds. However, wall clouds do not always rotate.

Wall clouds are formed by a process known as entrainment, when an inflow of warm, moist air rises and converges, overpowering wet, rain-cooled air from the normally downwind downdraft. As the warm air continues to entrain the cooler air, the air temperature drops and dew point increases. As this air continues to rise, it becomes more saturated with moisture, which results in additional clouds, usually in the form of a wall cloud. Wall clouds may form as a descending of the cloud base or may form as rising scud comes together and connects to the storm's cloud base.Also the cool air rushes upwards when meets a wall cloud.