Volutus are usually formed at the boundary layer. When the warm air upwards, they push the surrounding cold air upwards. After the two are mixed, the temperature around the storm will drop. After the upward hot air and the downward cold air convection, before the storm, a wave-like cloud will form. When the storm approaches, the clouds formed by the cooler downward air currents will evaporate. At this moment, the clouds will expand to form a roller cloud.