Cirrostratus: the high veil that draws a halo

Start with the shape: Cirrostratus (Cs) is a transparent, whitish veil made mainly of small ice crystals. The veil can look smooth or fibrous, cover part or all of the sky, and often produces a halo around the Sun or Moon. 1

The field check is simple: look for a connected high-level sheet, keep the solar or lunar disc in view, and scan for rings, arcs, or bright side spots. Cirrostratus is usually found around 20,000–40,000 feet in temperate regions, although high-cloud levels shift with latitude. 2

Cirrostratus often forms as air rises slowly and spreads ahead of a frontal system. The cloud itself brings no precipitation to the ground, but a widening, thickening veil can signal a larger change aloft. A warm-front rain arrival within about a day is a rule of thumb, not a guarantee. 3

The last card gives the practical split: a veil points to cirrostratus, detached filaments point to cirrus, and a greyer middle-level sheet with a blurred Sun points to altostratus. 4