Cloud height estimation | Previous Top Next

In the absence of instrumental aids the cloud-base height must be estimated. In order to improve their ability to do this, observers should be encouraged to take every opportunity of checking their estimates against known heights, e.g. when a cloud base is seen to intercept a mountainous coast (although in such circumstances the cloud base may be lower at the mountain than at sea). At stations where the observer has reports available from aircraft descending or ascending in the vicinity he can relate these to what he sees and so provide reports sufficiently reliable for meteorological purposes. At other stations estimates can sometimes be widely in error.
As a rough guide, the heights of the bases of the various types may be expected to be between the following limits:
Low Clouds (Cl)
Stratus: usually below 600 m (2000 ft) and sometimes nearly down to the surface.
Cumulonimbus: 600 - 1500 m (2000 - 5000 ft).
Stratocumulus: 450 - 1350 m (1500 - 4500 ft).
Cumulus: 450 - 1500 m (1500 - 5000 ft).
Middle Clouds (Cm)
Nimbostratus: 150 - 2000 m (500 - 6500 ft), usually below 600 m (2000 ft) in moderate rain or snow.
Altostratus and Altocumulus: 2000 - 5500 m (6500 - 18000 ft).
High Clouds (Ch)
usually above 5500 m (18000 ft).
Note

- These limits tend to be considerably higher in low latitudes; this applies particularly to high clouds.

Note (auxiliary ships only)

- Auxiliary ships do not report the height of base of lowest cloud in the sky.