Definitions for "Sky cover"
Clear Zero to 1/10 opaque cloud cover. Mostly Sunny 1/10 to 2/10 opaque cloud cover. The prevailing condition is sunny, but some clouds may be present either over a portion of the area or for a short time over the entire area. Fair Less than 4/10 opaque cloud cover. No precipitation. No extremes in weather, visibility, temperature, or wind. Partly cloudy/partly sunny 3/10 to 6/10 opaque cloud cover. Mostly cloudy/considerable cloudiness 7/10 to 8/10 opaque cloud cover. Cloudiness will be subject to some variability in amount or location. Cloudy 9/10 or greater opaque cloud cover. The sky is essentially covered throughout the forecast period.
The amount of the sky which is covered by clouds or obscurations in contact with the surface.
The amount of sky covered or concealed by clouds or obscuring phenomena. It is reported in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky. The following classifications are used in aviation weather observations: clear, scattered, broken, overcast, partial obscuration, obscuration.