Aeronautical Terms beginning with O

Obscuration

Denotes sky hidden by surface-based. obscuring phenomena and vertical visibility restricted overhead.

Obscuring phenomena

Any hydrometeor or lithometeor other than clouds; may be surface based or aloft.

Occlusion

Same as occluded front—a composite of two fronts as a cold front overtakes a warm front or quasi-stationary front. (commonly called occlusion or frontal occlusion).

Occluded front

A composite of two fronts as a cold front overtakes a warm front or quasi-stationary front. (commonly called occlusion or frontal occlusion).

Orographic

Of, pertaining to, or caused by mountains as in orographic clouds, orographic lift, or orographic precipitation.

Ozone

An unstable form of oxygen; heaviest concentrations are in the stratosphere; corrosive to some metals; absorbs most ultraviolet solar radiation.