From Glossary of Meteorology


  1. Descriptive of a sky cover of 1.0 (95% or more) when at least a portion of this amount is attributable to clouds or obscuring phenomena aloft; that is, when the total sky cover is not due entirely to surface-based obscuring phenomena.

    In aviation weather observations, an overcast sky cover is denoted by the symbol "symbol"; it may be explicitly identified as thin (predominantly transparent); otherwise a predominantly opaque status is implicit. An opaque overcast sky cover always constitutes a ceiling.
    See obscuration.

  2. Popularly, the cloud layer that covers most or all of the sky.

    It generally suggests a widespread layer of clouds such as that considered typical of a warm front.