From Glossary of Meteorology
- (Also called obscured sky cover.) In U.S. weather observing practice, the designation for the sky cover when the sky is completely hidden by surface-based obscuring phenomena.
It is encoded "X" in aviation weather observations; it always constitutes a ceiling, the height of which is the value of vertical visibility into the obscuring phenomenon.
Compare partial obscuration.
- A surface-based obscuring phenomenon.