Clouds at the Beach

Shelf clouds, also known as arcus clouds, occur at the leading edge of thunderstorms. They announce the arrival of storms and, when combined with cumulonimbus thunderheads, can look like giant alien motherships. 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. https://earthsky.org/earth/photos-shelf-clouds-arcus/