Mid-level Clouds (between 2000 and 7000 m):

Most mid-level clouds are composed of liquid water droplets during summer and a liquid droplet/ice crystal mix during winter. Mid-level cloud names are preceded by the prefix "alto".

Altocumulus: These clouds are grey, puffy blobs, sometimes seen in parallel waves or bands. One part of the cloud is usually darker than the rest, which distinguishes altocumulus clouds from cirrocumulus clouds. Altocumulus clouds that look like "little castles" in the sky indicate rising air at the cloud level and often signal the approach of a thunderstorm.

Altostratus: These grey clouds cover the entire sky, usually extending over hundreds of square kilometres. The sun may be visible under thinner sections of the cloud as a dim, round disc, known as a "watery sun". Altostratus clouds usually form ahead of a storm that will bring widespread continuous precipitation.