Cloud Type

Cloud Type is a qualitative observation; clouds are fluid and do not always neatly match the categories humans have set up. They can be defined by their shape, the cloud base altitude, and whether they are producing precipitation. When observing cloud type look at all the clouds in the sky, in all directions. For each level, (low, mid, and high), identify the types of clouds that you see using the GLOBE Cloud Chart, the interactive dichotomous key, and the definitions found in Observing Cloud Type (shape and Height).

Cloud and Contrail Type Field Guide




Identifying and classifying clouds

Clouds are identified in twelve type classes. The names used for the clouds are based on three factors: their shape, the altitude at which they occur, and whether they are producing precipitation.


  1. Clouds come in three basic shapes:
    • cumulus clouds (heaped and puffy)
    • stratus clouds (layered)
    • cirrus clouds (wispy)
  2. Clouds occur in three altitude ranges (specifically, the altitude of the cloud base):
    • High clouds (base above 6,000 m); designated by "cirrus" or "cirro-"
      • Cirrus
      • Cirrocumulus
      • Cirrostratus
    • Middle clouds (base between 2,000 - 6,000 m); designated by "alto-"
      • Altocumulus
      • Altostratus
    • Low clouds (base below 2,000 m); no prefix
      • Stratus
      • Nimbostratus
      • Cumulus
      • Stratocumulus
      • Cumulonimbus
      • Fog is a cloud so low it touches the ground
  3. Clouds whose names incorporate the word "nimbus" or the prefix "nimbo-" are clouds from which precipitation is falling.
  4. Contrails are clouds formed around the small particles (aerosols) which are in aircraft exhaust. When these persist after the passage of the plane they are indeed clouds, and are of great interest to researchers. Under the right conditions, clouds initiated by passing aircraft can spread with time to cover the whole sky. The presence of contrails should be specifically flagged in your observations.

NOTE: While both cumulus and cumulonimbus clouds may have their bases starting below 2,000 m, they often grow thick enough to extend into the middle or even high range. Thus, they are often referred to as "clouds of vertical development". Viewed from satellites, which see the top of clouds, these will generally be classified as mid- or high-level clouds.