A diffuse, veil-like layer of ice crystal
s at high altitude
, sometimes miles thick. Very often gives rise to a 22º halo
, and every once in a while a 46º halo
; this is one way to tell a cirrostratus from an altostratus
, which is veil-like cloud mainly composed of liquid water. A cirrostratus is often associated with the coming of low pressure
, so wind
frequently occur within a day or so of its being seen.
Occasionally written cirro-stratus.