Cirrostratus clouds are thin, high-level clouds that form above 20,000 feet (6,000 meters) in the atmosphere. They are composed of ice crystals and have a transparent or translucent appearance, which allows the sun or moon to shine through them.
Cirrostratus clouds often form ahead of a warm front or a tropical cyclone, and can be a sign of approaching inclement weather. As they thicken, they can cause a halo effect around the sun or moon, known as a “sun halo” or “moon halo.”
Cirrostratus clouds are classified as “high clouds” along with other clouds that form at similar altitudes, such as cirrus clouds and cirrocumulus clouds. They are important to meteorologists because they can indicate the approach of a weather system, and can also influence the amount of solar radiation that reaches the Earth’s surface.