Altostratus Cloud

Altostratus Cloud

Altostratus is a cloud belonging to a class characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque. They can look similar to lower altitude stratus clouds.

Altostratus clouds are formed by the rising of a large air mass that condenses into a cloud. They can produce light precipitation, often in the form of virga. If the precipitation increases in persistence and intensity, the altostratus cloud may thicken into 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 signals the approach of a weakened or upper level warm front.