Stratus cloud classified as pannus clouds. Stratus only has one mutatus mother cloud. Stratus stratocumulomutatus clouds occur when stratocumulus opacus patches fuse to create a stratiform layer. Stratus clouds don't produce accessory clouds, but a supplementary feature praecipitatio is derived from Latin, which means "precipitation". Stratus clouds are too low to produce virga, or rain shears that evaporate before reaching the ground. A stratus cloud can form from stratocumulus spreading out under an inversion, indicating a continuation of prolonged cloudy weather with drizzle for several hours and then an improvement as it breaks into stratocumulus. Stratus clouds can persist for days in
Altostratus cloud nimbostratus. Altostratus most often takes the form of a featureless sheet of cloud but can be wavy (undulatus) as a result of wind shear through the cloud. It can also be fragmented (fibratus) with clear sky visible, which often the approach of a weakened or upper level warm front. Altostratus can be composed of ice crystals. In some ice crystal altostratus, very thin, rapidly disappearing horizontal sheets of water droplets appear at random. The sizes of the ice crystals in the cloud tended to increase as altitude decreased. However, close to the bottom of the cloud, the particles decreased in