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How much of the station circle is filled — eighths of the sky.
Also known as: Cloud cover symbol, Circle filled in on a weather map
The sky is divided into eight parts and the circle is shaded to match. An empty circle is clear, a filled one is overcast, and a circle with a cross through it means the sky could not be seen at all — which is information rather than a missing observation.
Cloud cover recorded in eighths of the sky and plotted by shading the station circle: empty for clear, a quarter filled for two oktas, half for four, and wholly filled for eight.
Contexts: Maps
A circle crossed by a line means the sky was obscured — by fog, heavy precipitation or blowing snow — which is a different statement from missing data and is coded separately.
Obscured is an observation. A blank station is not.
An estimate of the whole visible sky rather than a measurement, made historically by eye and now often by instrument, which is why it is reported in eighths and not in percentages.
A small circle filled by a quarter, a half, three-quarters or entirely in black, or crossed by a diagonal line.