BROKEN LAYER A cloud layer covering whose summation amount of sky cover is 5/8
CALM A condition when no motion of the air is detected.
CEILING The height above the Earth's surface (field elevation or ground elevation) of the
lowest non-surface based layer that is reported as broken or overcast, or the vertical visibility
into an indefinite ceiling.
CEILOMETER A device used to evaluate the height of clouds or the vertical visibility into a
CELSIUS The ninth General Conference of Weights and Measures, held in October 1948,
adopted the name Celsius in place of centigrade in honor of its originator, Anders Celsius (1704-
1744), a Swedish astronomer who devised the scale.
CLEAR-AIR TURBULENCE (CAT) Turbulence encountered when flying through air devoid
of clouds, produced primarily by thermals and wind shear, including proximity to the jet stream.
CLEAR SKY (SKC) The state of the sky when it is cloudless.
CLOUD-AIR LIGHTNING (CA) Streaks of lightning which pass from a cloud to the air, but
do not strike the ground.
CLOUD-CLOUD LIGHTNING (CC) Streaks of lightning reaching from one cloud to another.
CLOUD-GROUND LIGHTNING (CG) Lightning occurring between cloud and ground.
CLOUD HEIGHT The height of the base of a cloud or cloud layer above the surface of the
CONTOUR LINE A line connecting points of equal (constant) height on a Constant-Pressure
COORDINATED UNIVERSAL TIME (UTC) The time in the zero meridian time zone.
CUMULUS A principal cloud type in the form of individual, detached elements that are
generally dense and possess sharp non-fibrous outlines.
CUMULONIMBUS An exceptionally dense and vertically developed cloud, occurring either
isolated or as a line or wall of clouds with separated upper portions. These clouds appear as
mountains or huge towers, at least a part of the upper portions of which are usually smooth,
fibrous, or striated, and almost flattened.
DESIGNATED RVR RUNWAY A runway at civilian airports designated by the FAA for
reporting RVR in long-line transmissions.
Glossary of Selected Meteorological Terms