Altostratus

Altostratus is usually composed of water droplets but may be mixed with ice crystals at higher altitudes.

Cirrocumulus in its pure form is actually a high cumuliform genus, and cirrostratus is stratiform, like altostratus and lower based sheet clouds.

If the altocumulus is mixed with moisture-laden altostratus, the precipitation may reach the ground.

Mid-level altostratus and multi-level nimbostratus always have a flat or diffuse appearance and are therefore not subdivided into species.

The stratiform group is cross-classified into the genera cirrostratus (high-étage), altostratus (middle-étage), stratus (low-étage), and nimbostratus (multi-étage).

The sun and moon are visible in clear outline. citation Cirrostratus often thickens into altostratus ahead of a warm front or low-pressure area.

The variety undulatus (having a wavy undulating base) can occur with any clouds of the species stratiformis or lenticularis, and with altostratus.

This cloud often forms under a precipitating deck of altostratus or high-based nimbostratus associated with a well-developed warm front, slow-moving cold front, or low-pressure area.

Virga is a feature seen with clouds producing precipitation that evaporates before reaching the ground, these being of the genera cirrocumulus, altocumulus, altostratus, nimbostratus, stratocumulus, cumulus, and cumulonimbus.

Widespread opaque altostratus can produce light continuous or intermittent precipitation. citation Precipitation commonly becomes heavier and more widespread if it thickens into nimbostratus.