In
aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot a ...
, ceiling is a measurement of the height of the base of the lowest clouds (not to be confused with
cloud base
A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to ...
which has a specific definition) that cover more than half of the sky (more than 4
oktas
In meteorology, an okta is a unit of measurement used to describe the amount of cloud cover at any given location such as a weather station. Sky conditions are estimated in terms of how many eighths of the sky are covered in cloud, ranging from ...
) relative to the ground. Ceiling is not specifically reported as part of the
METAR (METeorological Aviation Report) used for flight planning by pilots worldwide, but can be deduced from the lowest height with broken (BKN) or overcast (OVC) reported. A ceiling listed as "unlimited" means either that the sky is mostly free of cloud cover, or that the cloud is high enough not to impede Visual Flight Rules (
VFR) operation.
Definitions
;
ICAO : The height above the ground or water of the base of the lowest layer of cloud below 6000 meters (20,000 feet) covering more than half the sky.
; United Kingdom : The vertical distance from the elevation of an aerodrome to the lowest part of any cloud visible from the aerodrome which is sufficient to obscure more than half of the sky.
; United States : The height 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.
[Section 1.1 14 CFR Part 1 - Definitions - Federal Air Regulations]
See also
*
Cloud base
A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to ...
References
{{DEFAULTSORT:Ceiling (Cloud)
Aviation meteorology