(1) Canada: The lesser of:

(a) the height above ground or water of the base of the lowest layer of cloud covering more than half the sky; or

(b) the vertical visibility in a surface-based layer which completely obscures the sky.

(2) ICAO: The height above the ground or water of the base of the lowest layer of cloud below 6000 m (20 000 ft) covering more than half the sky.

(3) U.S.: The heights above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as "broken," "overcast," or "obscuration," and not classified as "thin" or "partial."