Cirrostratus clouds are thin, ice-crystal clouds that form high in the atmosphere, typically at altitudes of 20,000 feet (6,000 meters) or more. They often cover the sky in a uniform layer, creating a milky appearance. These clouds can produce a halo effect around the sun or moon due to the refraction of light through the ice crystals. These clouds usually indicate that precipitation is on the way, often signaling the approach of a warm front. While they may not bring significant rain themselves, they can precede nimbostratus clouds, which are responsible for steady, prolonged rainfall.