Video: A shelf cloud formation as seen from the Diego Martin highway earlier this morning. Shelf clouds, also known as arcus clouds, occur at the leading edge of thunderstorms. Shelf clouds form when the cooler air of a thunderstorm encounters warm, humid air and lifts it. As the shelf cloud passes over you, you’ll notice a drop in temperature, and winds pick up as the gust front moves through. Rain follows soon behind. | T&T Weather Central

Arcus Clouds: What They Are And How They Form