Cirrostratus /ˌsɪroʊˈstrɑːtəs/ is a high-altitude, very thin, generally uniform stratiform genus-type of cloud.

On the approach of a frontal system, the cirrostratus often begins as nebulous and turns to fibratus.

If the cirrostratus begins as fragmented of clouds in the sky it often means the front is weak.

[2] Clouds resembling cirrostratus occasionally form in polar regions of the lower stratosphere.

Polar stratospheric clouds can take on this appearance when composed of tiny supercooled droplets of water or nitric acid.