How do altostratus clouds form? Altostratus layers are often composed of both water and ice and usually form when a layer of cirrostratus descends from a higher level. The Sun often cannot cast shadows when shining through altostratus clouds.

What causes altostratus clouds?

Altostratus is formed by the lifting of a large mostly stable air mass that causes invisible water vapor to condense into cloud. It 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.

Where can altostratus be found?

Definition: Sheet of featureless, gray clouds in the middle cloud level capable of masking the sun. Description & Characteristics. Altostratus clouds are found in the middle cloud level. And unlike their altocumulus counterpart, they're often boring to look at.