Definition
A cloud layer that covers the entire sky, or 8/8 (eight oktas) of the celestial dome, as observed from a given point on the ground. Reported in aviation weather as 'OVC' followed by the height of the cloud base above ground level in hundreds of feet.
Plain English
A sheet of cloud that covers the whole sky above you, with no breaks. Weather reports show it as OVC plus the height of the bottom of the cloud.
Context Anchor
Seen when planning or flying visually above clouds, especially when deciding whether there will be a safe way to climb above or descend below the clouds.
Derivation
Overcast' comes from the older English sense of 'cast over' — something thrown or spread across the top of another thing. The sky is 'cast over' completely by cloud. This helps reinforce the idea of full coverage rather than partial cloud.
Why Pilots Care
Determines whether VFR over-the-top flight is possible, since regulations require the ability to return to visual conditions.
Grounding Statement
Picture being above a white sheet of clouds with no holes showing the ground below.
Intuition Check
Overcast does not just mean gray or gloomy weather. In aviation weather reporting, it means the cloud layer covers the whole sky from the reporting point.
Example Sentence 1
The METAR reported OVC025, so the overcast layer formed a ceiling at 2,500 feet above the airport.
Example Sentence 2
Once the aircraft climbed above the overcast layer the pilot maintained VFR in clear air while the ground remained hidden below.