Cap
(or Capping Inversion) - a layer of relatively
warm air aloft (usually several thousand feet above the ground) which suppresses
or delays the development of thunderstorms
CAPE
(Convective Available Potential Energy) -
a measure of the amount of energy available for
convection. CAPE is directly related to the maximum
potential vertical speed within an updraft; thus,
higher values indicate greater potential for severe weather. Observed values
in thunderstorm environments often may exceed
1,000 Joules per kilogram (J/kg), and in extreme cases may exceed 5,000 J/kg.
Carbon
Dioxide - CO2; a colorless
and odorless gas which is the fourth most abundant
constituent of dry air
Cb
- short for Cumulonimbus cloud;
known colloquially as a "thunderhead"
CC
- cloud-to -cloud lightning
Cc
- short for Cirrocumulus
CCL
- acronym for convective condensation level
Ceiling
- The height above the earth's surface given to the lowest cloud
layer or obscuring phenomena when
the sky cover is reported as broken,
overcast, or obscuration
and not classified "thin" or "partial." See vertical
visibility.
Ceilometer
- an automatic, recording, cloud-height
indicator. A light is projected upward onto the cloud base; the reflected light
is detected by a photocell, and the height is determined by triangulation (the
unique point where three line meet).
Cell
- convection in the form of a single updraft,
downdraft, or updraft/downdraft couplet, typically
seen as a vertical dome or tower as in a cumulus or towering
cumulus cloud
Celsius
Scale - temperature scale on which
the interval between the freezing point and the boiling
point of water is divided into 100 degrees, with 0 degrees representing
the freezing point and 100 degrees the boiling point
CG
- a cloud-to -ground lightning
flash
Charles'
Law - in a gaseous system at constant pressure, the temperature
increase and relative volume increase are proportionally the same for
all perfect gases. Named for Jacques Charles
(1746 - 1823), a French chemist.
Chinook
Wind - a warm, dry wind that descends the
eastern slopes of the Rocky Mountains
Ci-
abbreviation for cirrus clouds
CIN
(Convective INhibition) - a measure of the amount of
energy needed to initiate convection;
values of CIN typically reflect the strength of the cap
Cirrocumulus
- a high-level cloud which is composed mostly
of ice crystals and has the appearance of a
thin, white patch of rippled cloud
Cirrostratus
- a high-level cloud which is composed mostly
of ice crystals and has the appearance of a
whitish veil which may totally cover the sky
Cirrus
- a high-level cloud (16,000 feet or more) which
is composed mostly of ice crystals and has the
appearance of white, delicate filaments in patches or narrow bands
Clausisus-Clapeyron
equation - the equation showing the relationship between pressure
and temperature where two phases of a substance (liquid water and water
vapor) are in equilibrium. Named for
Rudolph Clausius (1822 -1888), a German physicist, and Benoit-Pierre-Emile
Clapeyron (1799 - 1864), a French engineer.
Clear-air
Mode - a highly sensitive operational mode of a WSR-88D
radar in which the antenna scans slowly, obtaining only 5 elevation slices in
10 minutes. This slow scan speed allows the radar to sense echoes from "clear-air"
(i.e., no precipitation). These echoes can be from dirt, insects, smoke, and
changes in the air density.
Clear
Air Turbulence (CAT) - in aviation, sudden severe turbulence
occurring in cloudless regions that causes violent buffeting of aircraft
Clear
Slot - a local region of clearing skies or
reduced cloud cover, indicating an intrusion of drier air; often seen as a bright
area with higher cloud bases on the west or southwest side of a wall
cloud. A clear slot is believed to be a visual indication of a rear
flank downdraft.
Climate
- the statistical collection of weather
conditions at a place over a period of years
Climatology
- the science that deals with climates and
their phenomena
Climometer
- an instrument that measures angles of inclination; used to
measure cloud ceiling heights
Closed
Low - a low pressure area with a distinct center of cyclonic
circulation which can be completely encircled by one or more isobars
or height contour lines. The term usually is used to
distinguish a low pressure area aloft from a low-pressure trough.
Cloud
- a visible mass of minute water and/or ice particles in the atmosphere
suspended above the earth's surface
Cloud
Base- the lowest level in the atmosphere that contains cloud particles
(water droplets, ice crystals, etc.)
Cloud
Height- the altitude of the cloud base above
the local terrain or the difference in height between the cloud top and the
cloud base; (sometimes called "thickness or "depth"
of the cloud)
Cloud
Layer - a group of clouds, not necessarily of the same type, that
has the cloud bases at the same altitude
Cloud
Seeding - any technique carried out to introduce artificial substances
into the cloud with the intent of altering the natural
development of that cloud
Coherent
Radar - a radar in which the phase
of the transmitted radiation is known. A coherent
radar compares the phase of transmitted and received pulses, permiting target
velocities to be calculated using the Doppler
effect.
Cold
Advection (or Cold Air Advection) - the transport of cold air into
a region by horizontal winds
Cold-Air
Funnel - a funnel cloud or (rarely)
a small, relatively weak tornado that can develop
from a small shower or thunderstorm
when the air aloft is unusually cold (hence the name). They are much less violent
than other types of tornadoes.
Cold
Cloud - a cloud comprised of ice particles or
a mixture of ice particles and water droplets
Cold
Front - an advancing edge of a cold air
mass
Cold
Pool - a region of relatively cold air, represented on a weather
map analysis as a relative minimum in temperature surrounded by closed isotherms.
Cold pools aloft represent regions of relatively low stability,
while surface-based cold pools are regions of relatively stable air.
Comma
Cloud - a synoptic-scale cloud
pattern with a characteristic comma-like shape, often seen on satellite photographs
associated with large and intense low-pressure systems
Composite
Chart - a map constructed by overlaying critical values of
atmospheric parameters analyzed to assess severe weather potential. A
composite chart might indicate the position of low level moisture
axes, a surface temperature ridge,
a 300 mb jet stream, and a 500 mb height trough.
Composite
Reflectivity - the maximum reflectivity
in a vertical column. This product is obtained by comparing several individual
tilts, or scans, of the radar, each one successively
looking at different elevations in the atmosphere.
Condensation
- the physical process by which a gas becomes
a liquid; the opposite of evaporation
Condensation
Funnel - a funnel-shaped cloud associated
with rotation and consisting of condensed water droplets (as opposed to smoke,
dust, debris, etc.)
Condensation
Nucleus - a particle in the atmosphere, either liquid or solid, upon
which condensation of water vapor begins
Conduction
- the transfer of energy
by molecular motion from warmer to colder regions through a substance or between
objects in direct contact, and without any net external motion
Cone-of-silence
- an area directly above and surrounding the radar where the radar
does not sample the atmosphere. This is an artifact
of the particular VCP that is used by the radar.
Confluence
- a pattern of wind flow in which air flows inward toward an axis oriented
parallel to the general direction of flow; the opposite of difluence.
Confluence is not the same as convergence.
Congestus
(or Cumulus Congestus) - same as towering
cumulus
Conservation
of Energy - a law of physics that states that energy
can not be created or destroyed only converted from one form to another
Conservation
of Mass - a law of physics that states that mass can not be created
or destroyed only transferred from one volume to another
Conservation
of Momentum - a law of physics that states that an object in motion
will stay in motion until acted upon by an outside force;
an object at rest will remain at rest until acted upon by an outside force
Continental
Arctic Air Mass - an air mass characterized
by extremely cold, dry air
Continental
Polar Air Mass - an air mass characterized
by cold, dry air
Continental
Tropical Air Mass - an air mass characterized
by warm or hot dry air
Contour
Line - generally, a line of constant value; in meteorology, typically
refers to a line of constant elevation above a specified reference level (usually
mean sea level)
Contrail
(or Condensation Trail) - streaks
of condensed water vapor created in the air
behind aircraft flying in clear, cold, humid air
Convection
- in general, the transport and mixing of the properties of a fluid
(e.g., heat, moisture, etc.) by means of mass motion
within the fluid; in meteorology, atmospheric motions generally are divided
into those in the horizontal, or advection, and those in the vertical, or convection;
convection typically results from surface heating and the subsequent rising
of warm air
Convective
Cloud - a cloud which develops vertically by convection
Convective
Condensation Level (CCL) - the level in the atmosphere
to which an air parcel, if heated from below,
will rise dry adiabatically, without becoming colder than its environment just
before the parcel becomes saturated. See Lifted
Condensation Level (LCL).
Convective
Outlook (sometimes called AC) - a forecast containing the area(s)
of expected thunderstorm occurrence and expected
severity over the contiguous United States, issued several times daily by the
SPC
Convective
Temperature - the approximate temperature
that the air near the ground must warm to in order for surface-based convection
to develop
Conventional
Weather Radar - a weather radar that
measures only the intensity of returned radiation,
or reflectivity.
Convergence
- the net inflow of air into a region, typically caused by horizontal
wind motion; the opposite of divergence
Cooling
Degree-Day - a type of degree day
used for estimating energy requirements for cooling the indoor environment to
a base temperature, generally to 65 degrees
Fahrenheit; one cooling degree-day is given
for each degree that the day's average temperature is above the base temperature
Coriolis
Force - an apparent force that
as a result of the earth's rotation deflects objects moving above the
earth's surface to the right in the Northern Hemisphere and to the left
in the Southern Hemisphere
Corona
- the set of colored rings around the sun (or moon) created
when it shines through a thin cloud
Crepuscular
Rays - the alternating bands of light and dark (rays and shadows)
seen at the earth's surface when the sun shines through clouds
Cumulonimbus
- exceptionally dense and vertically developed cloud
type, occurring both as isolated clouds and as a line or wall of clouds, and
generally accompanied by heavy rain, lightning,
and thunder
Cumulus
- cloud type in the form of individual, detached
elements which are generally dense, have well-defined outlines, show vertical
development in the form of domes, mounds, or towers
Cumulus
Congestus (or simply Congestus) - same as towering
cumulus
Cutoff
Low - a closed low which has become completely
displaced (cut off) from the basic westerly current, and moves independently
of that current. Cutoff lows may remain nearly stationary for days, or on occasion
may move westward -- opposite to the prevailing flow aloft.
Cyclogenesis
- the development or intensification of a low-pressure center (cyclone)
Cyclone
- an atmospheric circulation that rotates counter-clockwise in the
Northern Hemisphere and clockwise in the Southern Hemisphere, that usually has
a diameter of 2000 to 3000 kilometers
Cyclonic
Rotation - rotation in the same sense as the earth's rotation (i.e.,
counter-clockwise in the Northern Hemisphere as would be seen from above); the
opposite of anticyclonic rotation
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