Plain English Meaning

How low the clouds are and how far you can see. These two numbers together tell a pilot whether the weather is good enough to fly by looking outside, or whether they’ll need to fly using instruments — or stay on the ground.

Full Definition

A combined weather assessment that describes two key conditions for flight: the ceiling — the height above the ground of the lowest layer of clouds reported as broken or overcast (or the vertical visibility into an obscuration) — and the visibility, which is the greatest horizontal distance at which prominent objects can be seen and identified. Together they define how much usable airspace and forward sight a pilot has, and they determine whether flight can be conducted under () or requires ().