Conditions

(Section 2.8.1.1)

The selection of the correct code figures requires the following and must be noted:

1. Observation of the sky as a whole:

• This arises from the fact that certain code specifications apply not only to the particular genera, species or varieties of the individual clouds, but also to the aspect of the sky as a whole
• In addition, there are situations in which the aspect of the sky as a whole is immediately recognizable, whereas the cloud forms present are difficult to identify

2. An almost continuous watch on the sky:

• This stems from the fact that certain code specifications are directly related to the evolution and development of individual clouds or of the total cloud cover; an almost continuous watch on the sky is also necessary in situations when the appearance of the sky at the time of observation is so confusing that it is impossible to select the correct code figure, except by relating the existing transitional cloud forms with the characteristic forms from which they evolved
• The C_L code indicates clouds of the genera Stratocumulus, Stratus, Cumulus and Cumulonimbus
• The C_M code indicates clouds of the genera Altocumulus, Altostratus and Nimbostratus
• The C_H code indicates clouds of the genera Cirrus, Cirrocumulus and Cirrostratus