The unit for cloud cover, how many eighths of the sky are covered by cloud, from 0 to 8.
An okta is one eighth of the sky. Cloud cover is given in oktas from 0 to 8: 0 means a completely clear sky, 8 means fully overcast. Observers estimate it by eye, imagining the sky divided into eight equal parts.
The scale
| Oktas | Sky |
|---|---|
| 0 | Clear |
| 1–2 | A few clouds |
| 3–4 | Scattered clouds |
| 5–7 | Broken cloud, mostly covered |
| 8 | Overcast |
In weather observations, the code 9 is used when the sky can't be seen at all, for example in fog. Aviation reports use the same groups as abbreviations: FEW (1–2), SCT (3–4), BKN (5–7) and OVC (8).
On board
Cloud cover belongs in the weather column of a logbook, next to wind, sea state, visibility and barometer. Noted every few hours, it shows how the weather develops: cloud thickening from the west, for example, often comes ahead of a front.
Manta does this for you
Weather log for every sailing trip
Every trip shows wind, sea state and weather for each hour. Where your instruments are silent, Apple Weather fills the gaps.
