Subj : Weather Glossary (C)
To : All
From : Daryl Stout
Date : Sun Aug 04 2019 12:02 am
This weather glossary contains information on more than 2000 terms,
phrases and abbreviations used by the National Weather Service (NWS)...
the government agency who makes weather forecasts, and issues weather
advisories, watches, and warnings, for the United States, and its
territories.
Many of these terms and abbreviations are used by NWS forecasters to
communicate between each other and have been in use for many years and
before many NWS products were directly available to the public. It is the
purpose of this glossary to aid you in better understanding NWS products.
***
C
1. Degrees Celsius (?C)
2. Central
C AMS
Continental Air Mass
CA
Cloud-to-Air lightning.
CAA
Cold Air Advection
CAD
Cold Air Damming. The phenomenon in which a low-level cold air mass is
trapped topographically. Often, this cold air is entrenched on the east
side of mountainous terrain. Cold Air Damming often implies that the
trapped cold air mass is influencing the dynamics of the overlying air
mass, e.g. in an overrunning scenario. Effects on the weather may include
cold temperatures, freezing precipitation, and extensive cloud cover.
CADAS
Centralized Automated Data Acquisition System - a system of two
minicomputers in NWSH.
Calibration
In hydrologic terms, the process of using historical data to estimate
parameters in a hydrologic forecast technique such as SACSMA, routings,
and unit hydrographs.
Calm
A weather condition when no air motion (wind) is detected.
Canyon Wind
A foehn wind that is channeled through a canyon as it descends the lee
side of a mountain barrier.
Cap
(also called "Lid") A layer of relatively warm air aloft, usually several
thousand feet above the ground, which suppresses or delays the development
of thunderstorms. Air parcels rising into this layer become cooler than
the surrounding air, which inhibits their ability to rise further and
produce thunderstorms. As such, the cap often prevents or delays
thunderstorm development even in the presence of extreme instability.
However, if the cap is removed or weakened, then explosive thunderstorm
development can occur.
The cap is an important ingredient in most severe thunderstorm episodes,
as it serves to separate warm, moist air below and cooler, drier air
above. With the cap in place, air below it can continue to warm and/or
moisten, thus increasing the amount of potential instability. Or, air
above it can cool, which also increases potential instability. But
without a cap, either process (warming/moistening at low levels or
cooling aloft) results in a faster release of available instability -
often before instability levels become large enough to support severe
weather development.
Cap Cloud
A stationary cloud directly above an isolated mountain peak, with cloud
base below the elevation of the peak.
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 1000 joules per kilogram (J/kg), and in
extreme cases may exceed 5000 J/kg.
However, as with other indices or indicators, there are no threshold
values above which severe weather becomes imminent. CAPE is represented
on an upper air sounding by the area enclosed between the environmental
temperature profile and the path of a rising air parcel, over the layer
within which the latter is warmer than the former. (This area often is
called positive area.) See also CIN.
Capillarity
In hydrologic terms,
1.The degree to which a material or object containing minute openings or
passages, when immersed in a liquid, will draw the surface of the liquid
above the hydrostatic level. Unless otherwise defined, the liquid is
generally assumed to be water.
2. The phenomenon by which water is held in interstices above the normal
hydrostatic level, due to attraction between water molecules.
Capillary Fringe
In hydrologic terms, the soil area just above the water table where water
can rise up slightly through the cohesive force of capillary action. This
layer ranges in depth from a couple of inches, to a few feet, and it
depends on the pore sizes of the materials. The capillary fringe is also
called the capillary zone.
Capillary Waves
Waves caused by the initial wind stress on the water surface causes what
are known as capillary waves. These have a wavelength of less than 1.73
cm, and the force that tries to restore them to equilibrium is the
cohesion of the individual molecules. Capillary waves are important in
starting the process of energy transfer from the air to the water.
Capillary Zone
Used interchangably with Capillary Fringe; the soil area just above the
water table where water can rise up slightly through the cohesive force
of capillary action. This layer ranges in depth from a couple of inches,
to a few feet, and it depends on the pore sizes of the materials.
Capping
A region of negative buoyancy below an existing level of free convection
(LFC) where energy must be supplied to the parcel to maintain its ascent.
This tends to inhibit the development of convection until some physical
mechanism can lift a parcel to its LFC. The intensity of the cap is
measured by its convective inhibition. The term capping inversion is
sometimes used, but an inversion is not necessary for the conditions
producing convective inhibition to exist.
Capping Inversion
Alternate term for Cap; a layer of relatively warm air aloft, usually
several thousand feet above the ground, which suppresses or delays the
development of thunderstorms. Air parcels rising into this layer become
cooler than the surrounding air, which inhibits their ability to rise
further and produce thunderstorms. As such, the cap often prevents or
delays thunderstorm development even in the presence of extreme
instability. However, if the cap is removed or weakened, then explosive
thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes,
as it serves to separate warm, moist air below and cooler, drier air
above. With the cap in place, air below it can continue to warm and/or
moisten, thus increasing the amount of potential instability. Or, air
above it can cool, which also increases potential instability. But
without a cap, either process (warming/moistening at low levels or
cooling aloft) results in a faster release of available instability -
often before instability levels become large enough to support severe
weather development.
CAPS
Center for Analysis and Prediction of Storms
Carbon Dioxide
CO2; a colorless and odorless gas which is the fourth most abundant
constituent of dry air.
Carrington Longitude
A system of fixed longitudes rotating with the sun.
Catalina Eddy
A Catalina Eddy (coastal eddy) forms when upper level large-scale flow
off Point Conception interacts with the complex topography of the
Southern California coastline. As a result, a counter clockwise
circulating low pressure area forms with its center in the vicinity of
Catalina Island. This formation is accompanied by a southerly shift in
coastal winds, a rapid increase in the depth of the marine layer, and a
thickening of the coastal stratus. Predominately these eddies occur
between April and September with a peak in June. A typical Catalina
eddy will allow coastal low clouds and fog to persist into the
afternoon. A strong Catalina eddy may extend to 6000 feet and these
clouds will move through the inland valleys and reach as far as
Palmdale.
Catchment Area
In hydrologic terms, an area having a common outlet for its surface
runoff (also see Drainage Area or Basin, Watershed).
Categorical
A National Weather Service precipitation descriptor for a 80, 90, or
100 percent chance of measurable precipitation (0.01 inch). See
Precipitation Probability (PoP)
CAVU
Clear or Scattered Clouds (visibility greater than 10 mi.)
Cb
Cumulonimbus cloud, characterized by strong vertical development in
the form of mountains or huge towers topped at least partially by a
smooth, flat, often fibrous anvil. Also known colloquially as a
"thunderhead."
CBMAM
Cumulonimbus Mamma
CC
Cloud-to-Cloud Lightning
CCITT
Consultative Committee for International Telephone and Telegraph
CCL
Convective Condensation Level- 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).
CD
cold
CDB
Computing Development Branch (NCEP)
CDC
Climate Diagnostic Center, the mission of the Climate Diagnostics
Center (CDC) is to advance national capabilities to interpret the
causes of observed climate variations, and to apply this knowledge to
improve climate models and forecasts and develop new climate products
that better serve the needs of the public and decision-makers.
CDD
Cooling Degree Days- A form of degree day used to estimate energy
requirements for air conditioning or refrigeration. Typically,
cooling degree days are calculated as how much warmer the mean
temperature at a location is than 65� F on a given day. For example,
if a location experiences a mean temperature of 75� F on a certain day,
there were 10 CDD (Cooling Degree Days) that day because 75 - 65 = 10.
CDFNT
Cold Front
CDT
Central Daylight Time
Ceiling
(Abbrev. CIG) - The height of the cloud base for the lowest broken or
overcast cloud layer.
Ceilometer
A device using a laser or other light source to determine the height of
a cloud base. An optical ceilometer uses triangulation to determine the
height of a spot of light projected onto the base of the cloud; a laser
ceilometer determines the height by measuring the time required for a
pulse of light to be scattered back from the cloud base.
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 towering cumulus cloud. A typical thunderstorm consists of
several cells.
The term "cell" also is used to describe the radar echo returned by an
individual shower or thunderstorm. Such usage, although common, is
technically incorrect.
Celsius
The standard scale used to measure temperature in most areas outside
the United States. On this scale, the freezing point of water is 0� F
and the boiling point is 100� F. To convert a Fahrenheit temperature to
Celsius, subtract 32 from it and then multiply by 5/9:
�C = (�F - 32) * 5/9
CEM
Civil Emergency Message. A message issued by the National Weather
Service in coordination with Federal, state or local government to warn
the general public of a non-weather related time-critical emergency
which threatens life or property, e.g. nuclear accident, toxic chemical
spill, etc.
Center
Generally speaking, the vertical axis of a tropical cyclone, usually
defined by the location of minimum wind or minimum pressure. The cyclone
center position can vary with altitude. In advisory products, refers to
the center position at the surface.
Centimeter Burst
A solar radio burst in the centimeter wavelength range.
Central Meridian Passage (CMP)
In solar-terrestrial terms, the passage of an Active Region or other
feature across the longitude meridian that passes through the apparent
center of the solar disk.
CFC
Chlorofluorocarbon
CFP
Cold Front Passage
CFS
In hydrologic terms, Cubic Feet per Second - the flow rate or discharge
equal to one cubic foot (of water, usually) per second. This rate is
equivalent to approximately 7.48 gallons per second. This is also
referred to as a second-foot.
Cfs-Day
In hydrologic terms, the volume of water discharged in twenty four hours,
with a flow of one cubic foot per second is widely used; 1 cfs-day is
24 x 60 x 60 = 86,000 cubic feet, 1.983471 acre-feet, or 646,317 gallons.
The average flow in cubic feet per second for any time period is the
volume of flow in cfs-days.
CG
Cloud-to-Ground Lightning
Chance
A National Weather Service precipitation descriptor for 30, 40, or 50
percent chance of measurable precipitation (0.01 inch). When the
precipitation is convective in nature, the term scattered is used. See
Precipitation Probability (PoP).
Channel
In hydrologic terms, also known as Watercourse; an open conduit either
naturally or artificially created which periodically, or continuously
contains moving water, or forms a connecting link between two bodies of
water. River, creek, run, branch, anabranch, and tributary are some of
the terms used to describe natural channels. Natural channels may be
single or braided. Canal and floodway are some of the terms used to
describe artificial channels.
Channel Inflow
In hydrologic terms, water, which at any instant, is flowing into the
channel system form surface flow, subsurface flow, base flow, and
rainfall that has directly fallen onto the channel.
Channel Lead
In hydrologic terms, an elongated opening in the ice cover caused by a
water current.
Channel Routing
In hydrologic terms, the process of determining progressively timing
and shape of the flood wave at successive points along a river.
Channeled High Winds
In mountainous areas or in cities with tall buildings, air may be
channeled through constricted passages producing high winds. Santa Ana
winds and winds through passes from the cold Alaskan interior to the
sea are examples of these winds. Channeled high winds are local in
nature but can be extremely strong. These winds generally occur in
well-defined areas.
Channelization
In hydrologic terms, the modification of a natural river channel; may
include deepening, widening, or straightening.
CHC
Chance
Chemistry Model
A computer model used in air pollution investigations that simulates
chemical and photochemical reactions of the pollutants during their
transport and diffusion.
CHG
Change
CHGS
changes
Chinook
This is a region-specific term used for Foehn Winds in the lee of the
Rocky Mountains in the United States; Foehn Winds are warm, dry winds
that occur in the lee of high mountain ranges. It is a fairly common
wintertime phenomena in the mountainous west and in parts of Alaska.
These winds develop in well-defined areas and can be quite strong.
Chinook Arch
A foehn cloud formation appearing as a bank of altostratus clouds east
of the Rocky Mountains, heralding the approach of a chinook. It forms
in the rising portion of standing waves on the lee side of the
mountains. An observer underneath or east of the cloud sees an arch of
clear air between the cloud's leading edge and the mountains below.
The cloud appears to converge with the mountains to the north and south
due to a perspective effect.
Chlorofluorocarbons
(CFCs) - Manufactured substances used as coolants and computer-chip
cleaners. When these products break down they destroy stratospheric
ozone, creating the Antarctic Ozone Hole in the Southern Hemisphere
spring (Northern Hemisphere autumn). While no longer in use, their
long lifetime will lead to a very slow removal from the atmosphere.
Chromosphere
In solar-terrestrial terms, the layer of the solar atmosphere above the
photosphere and beneath the transition region and the corona.
Chromospheric Events
In solar-terrestrial terms, flares that are just Chromospheric Events
without Centimetric Bursts or Ionospheric Effects. (SID)
(Class C flare)
CI
Cirrus clouds- High-level clouds (16,000 feet or higher), composed of
ice crystals and appearing in the form of white, delicate filaments or
white or mostly white patches or narrow bands. Cirrus clouds typically
have a fibrous or hairlike appearance, and often are semi-transparent.
Thunderstorm anvils are a form of cirrus cloud, but most cirrus clouds
are not associated with thunderstorms.
CIG
Ceiling- The height of the lowest layer of clouds, when the sky is
broken or overcast.
CIN
Convective INhibition. A measure of the amount of energy needed in order
to initiate convection. Values of CIN typically reflect the strength of
the cap. They are obtained on a sounding by computing the area enclosed
between the environmental temperature profile and the path of a rising
air parcel, over the layer within which the latter is cooler than the
former. (This area sometimes is called negative area.) See CAPE.
CIO
Chief Information Officer
Circulation
The flow, or movement, of a fluid (e.g., water or air) in or through a g
iven area or volume.
Cirriform
High altitude ice clouds with a very thin wispy appearance.
Cirrocumulus
A cirriform cloud characterized by thin, white patches, each of which is
composed of very small granules or ripples. These clouds are of high
altitude (20,000-40,000 ft or 6000 -12,000 m).
Cirrostratus
A cloud of a class characterized by a composition of ice crystals and
often by the production of halo phenomena and appearing as a whitish and
usually somewhat fibrous veil, often covering the whole sky and sometimes
so thin as to be hardly discernible. These clouds are of high altitude
(20,000-40,000 ft or 6000 -12,000 m).
Cirrus
(abbrev. CI) High-level clouds (16,000 feet or higher), composed of ice
crystals and appearing in the form of white, delicate filaments or white
or mostly white patches or narrow bands. Cirrus clouds typically have a
fibrous or hairlike appearance, and often are semi-transparent.
Thunderstorm anvils are a form of cirrus cloud, but most cirrus clouds
are not associated with thunderstorms.
Civil Dawn
The time of morning at which the sun is 6� below the horizon. At
this time, there is enough light for objects to be distiguishable and
that outdoor activities can commence.
Civil Dusk
The time at which the sun is 6� below the horizon in the evening.
At this time objects are distinguishable but there is no longer enough
light to perform any outdoor activities.
Civil Emergency Message
(Abbrev. CEM) - A message issued by the National Weather Service in
coordination with Federal, state or local government to warn the general
public of a non-weather related time-critical emergency which threatens
life or property, e.g. nuclear accident, toxic chemical spill, etc.
CL
An abbreviation used on climate outlook maps issued by CPC to indicate
areas where equal chances of experiencing below-normal, normal, and
above-normal conditions are possible.
Class I Areas
Geographic areas designated by the Clean Air Act where only a small
amount or increment of air quality deterioration is permissible.
CLD
Cloud- A visible aggregate of minute water droplets or ice particles in
the atmosphere above the Earth's surface.
Clear Air Turbulence
(CAT) - In aviation, sudden severe turbulence occurring in cloudless
regions that causes violent buffeting of aircraft.
Clear Ice
A thin coating of ice on terrestrial objects, caused by rain that
freezes on impact. The ice is relatively transparent, as opposed to
rime ice, because of large drop size, rapid accretion of liquid water,
or slow dissipation of latent heat of fusion.
Clear Slot
With respect to severe thunderstorms, 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.
Client Agency
As used in connection with reimbursable National Weather Service (NWS)
fire weather services, a public fire service or wildlands management
agency, Federal or non-Federal, which requires and uses NWS fire and
forestry meteorological services.
Climate
The composite or generally prevailing weather conditions of a region,
throughout the year, averaged over a series of years.
Climate Change
A non-random change in climate that is measured over several decades or
longer. The change may be due to natural or human-induced causes.
Climate Diagnostics Bulletin
(CDB) - The monthly CPC Bulletin reports on the previous months' status
of the ocean-atmosphere climate system and provides various seasonal
ENSO-related outlooks. It is issued by the fifteenth of the month.
Climate Diagnostics Center
(CDC) - The mission of NOAA's Climate Diagnostics Center is to identify
the nature and causes for climate variations on time scales ranging from
a month to centuries.
Climate Model
Mathematical model for quantitatively describing, simulating, and
analyzing the interactions between the atmosphere and underlying
surface (e.g., ocean, land, and ice).
Climate Outlook
A climate outlook issued by the CPC gives probabilities that conditions,
averaged over a specified period, will be below-normal, normal, or
above-normal.
Climate Prediction Center
This Center is one of several centers under the National Centers for
Environmental Prediction (NCEP) part of the National Weather Service
(NWS) in the National Oceanic and Atmospheric Administration (NOAA). The
Center serves the public by assessing and forecasting the impacts of
short-term climate variability, emphasizing enhanced risks of
weather-related extreme events, for use in mitigating losses and
maximizing economic gains.
Climate System
The system consisting of the atmosphere (gases), hydrosphere (water),
lithosphere (solid rocky part of the Earth), and biosphere (living)
that determine the Earth's climate.
Climatological Outlook
An outlook based upon climatological statistics for a region,
abbreviated as CL on seasonal outlook maps. CL indicates that the
climate outlook has an equal chance of being above normal, normal, or
below normal.
Climatology
The science that deals with the phenomena of climates or climatic
conditions.
CLIMO
Climatology/Climatological
Climometer
An instrument that measures angles of inclination; used to measure
cloud ceiling heights.
Closed Basin
A basin draining to some depression or pond within its area, from which
water is lost only by evaporation or percolation. A basin without a
surface outlet for precipitation falling precipitation.
Closed Basin Lake Flooding
Flooding that occurs on lakes with either no outlet or a relatively
small one. Seasonal increases in rainfall cause the lake level to rise
faster than it can drain. The water may stay at flood stage for weeks,
months, or years.
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. Closed lows aloft typically are
partially or completely detached from the main westerly current, and
thus move relatively slowly (see Cutoff Low).
Cloud
(abbrev. CLD) A visible aggregate of minute water droplets or ice
particles in the atmosphere above the Earth's surface.
Cloud Ceiling
Same as Ceiling; the height of the cloud base for the lowest broken or
overcast cloud layer.
Cloud Condensation Nuclei
Small particles in the air on which water vapor condenses and forms
cloud droplets.
Cloud Layer
An array of clouds whose bases are at approximately the same level.
Cloud Movement
The direction toward which a cloud is moving.
Cloud Streets
Rows of cumulus or cumulus-type clouds aligned parallel to the
low-level flow. Cloud streets sometimes can be seen from the ground,
but are seen best on satellite photographs.
Cloud Tags
Ragged, detached cloud fragments; fractus or scud.
CLR
Clear
CLRG
Clearing
Clutter
Radar echoes that interfere with observation of desired signals on the
radar display.
CMPLT
Complete
CMPLX
Complex
CNIF
In hydrologic terms, Calibration Network Information Files.
CNTR
Center
CNTRL
Central
CNVG
Converge
CNVTV
Convective
Coalescence
The process by which water droplets in a cloud collide and come together
to form raindrops.
Coastal Waters
Includes the area from a line approximating the mean high water along
the mainland or island as far out as 100 nautical miles including the
bays, harbors and sounds.
Coastal Waters Forecast (CWF)
The marine forecast for areas, including bays, harbors, and sounds, from
a line approximating the mean high water mark (average height of high
water over a 19-year period) along the mainland or near shore islands
extending out to as much as 100 NM.
Coastal/Lakeshore Flood Advisory
Minor flooding is possible (i.e., over and above normal high tide levels.
Coastal/Lakeshore Flood Advisories are issued using the Coastal/Lakeshore
Hazard Message (CFW) product.
Coastal/Lakeshore Flood Warning
Flooding that will pose a serious threat to life and property is
occurring, imminent or highly likely. Coastal/Lakeshore Flood Warnings
are issued using the Coastal/Lakeshore Hazard Message (CFW) product.
Coastal/Lakeshore Flood Watch
Flooding with significant impacts is possible. Coastal/Lakeshore Flood
Watches are issued using the Coastal/Lakeshore Hazard Message (CFW)
product.
Coastal/Lakeshore Flooding
(i) (Oceanic) Coastal Flooding is the inundation of land areas adjacent
to bodies of salt water connected to the Atlantic Ocean, Pacific Ocean,
or Gulf of Mexico, caused by sea waters over and above normal tidal
action. This flooding may impact the immediate oceanfront, gulfs, bays,
back bays, sounds, and tidal portions of river mouths and inland tidal
waterways.
(ii) Lakeshore Flooding is the inundation of land areas adjacent to one
of the Great Lakes caused by lake water exceeding normal levels.
Lakeshore flooding impacts the immediate lakefront, bays, and the
interfaces of lakes and connecting waterways, such as rivers.
COE
In hydrologic terms, Corps of Engineers.
Cold Advection
Transport of cold air into a region by horizontal winds.
Cold Air Avalanche
Downslope flow pulsations that occur at more or less regular intervals as
cold air builds up on a peak or plateau, reaches a critical mass, and
then cascades down the slopes.
Cold Air Dam
A shallow cold air mass which is carried up the slope of a mountain
barrier, but with insufficient strength to surmount the barrier. The
cold air, trapped upwind of the barrier alters the effective terrain
configuration of the barrier to larger-scale approaching flows.
Cold Air Damming (CAD)
The phenomenon in which a low-level cold air mass is trapped
topographically. Often, this cold air is entrenched on the east side
of mountainous terrain. Cold Air Damming often implies that the trapped
cold air mass is influencing the dynamics of the overlying air mass,
e.g. in an overrunning scenario. Effects on the weather may include
cold temperatures, freezing precipitation, and extensive cloud cover.
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 Front
A zone separating two air masses, of which the cooler, denser mass is
advancing and replacing the warmer.
Cold Occlusion
A frontal zone formed when a cold front overtakes a warm front and,
being colder than the air ahead of the warm front, slides under the
warm front, lifting it aloft. Compare with warm occlusion.
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.
Collar Cloud
A generally circular ring of cloud that may be observed on rare
occasions surrounding the upper part of a wall cloud. This term
sometimes is used (incorrectly) as a synonym for wall cloud.
Collection Efficiency
The fraction of droplets approaching a surface that actually deposit
on that surface.
Colorado Low
A low pressure storm system that forms in winter in southeastern
Colorado or northeastern New Mexico and tracks northeastward across
the central plains of the U.S. over a period of several days,
producing blizzards and hazardous winter weather.
Columnar Ice
In hydrologic terms, ice consisting of columnar shaped grain. The
ordinary black ice is usually columnar-grained.
Combined Seas
Combination of both wind waves and swell. Also called "Seas" and is
approximately equal to significant wave height.
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.
Comma Echo
A thunderstorm radar echo which has a comma-like shape. It often
appears during latter stages in the life cycle of a bow echo.
Complex Gale/Storm
In the high seas and offshore forecasts, an area for which gale/storm
force winds are forecast or are occurring but for which no single
center is the principal generator of these winds.
Complex Terrain
Typically used to refer to mountainous terrain. In general usage, it
may also refer to coastal regions and heterogeneous landscapes.
Composite
An average that is calculated according to specific criteria. For
example, one might want a composite for the rainfall at a given
location for all years where the temperature was much above average.
Composite Hydrograph
A stream discharge hydrograph which includes base flow, or one which
corresponds to a net rain storm of duration longer than one unit
period.
Comprehensive Flare Index (CFI)
In solar-terrestrial terms, the indicative of solar flare importance.
Concentric Rings
These are common in the most intense hurricanes. They usually mark the
end of the period of intensification. These hurricanes then maintain
quasi-constant intensity or weaken. When the inner eye is completely
dissipated, more intensification may occur.
COND
Condition
Condensation
In general, the physical process by which a vapor becomes a liquid or
solid; the opposite of evaporation, although on the molecular scale,
both processes are always occurring.
Condensation Funnel
A funnel-shaped cloud associated with rotation and consisting of
condensed water droplets (as opposed to smoke, dust, debris, etc.).
Conditionally Unstable Air
An atmospheric condition that exists when the environmental lapse rate
is less than the dry adiabatic lapse rate but greater than the moist
adiabatic lapse rate.
Conduction
Flow of heat in response to a temperature gradient within an object or
between objects that are in physical contact.
Cone of Depression
In hydrologic terms, the depression, roughly conical in shape, produced
in a water table, or other piezometric surface, by the extraction of
water from a well at a given rate. The volume of the cone will vary
with the rate of withdrawal of water. Also called the Cone of Influence.
Cone of Influence
Same as Cone of Depression; in hydrologic terms, the depression, roughly
conical in shape, produced in a water table, or other piezometric surface,
by the extraction of water from a well at a given rate. The volume of the
cone will vary with the rate of withdrawal of water.
Confined Ground Water
In hydrologic terms, ground water held under an aquiclude or an aquifuge,
called artesian if the pressure is positive.
Confluence
A pattern of wind flow in which air flows inward toward an axis oriented
parallel to the general direction of flow. It is the opposite of
difluence. Confluence is not the same as convergence. Winds often
accelerate as they enter a confluent zone, resulting in speed divergence
which offsets the (apparent) converging effect of the confluent flow.
Congestus
(or Cumulus Congestus) - same as towering cumulus.
Congressional Organic Act of 1890
The act that assigned the responsibility of river and floor forecasting
for the benefit of the general welfare of the Nation's people and
economy to the Weather Bureau, and subsequently the National Weather
Service.
Coning
With regards to wildfires, pattern of plume dispersion in a neutral
atmosphere, in which the plume attains the form of a cone with its
vertex at the top of the stack.
Conjugate Points
Two points on the earth's surface, at opposite ends of a geomagnetic
field line.
Conservation Storage
In hydrologic terms, storage of water for later release for usual
purposes such as municipal water supply, power, or irrigation in
contrast with storage capacity used for flood control.
Consolidated Ice Cover
In hydrologic terms, ice cover formed by the packing and freezing
together of floes, brash ice and other forms of floating ice.
Constant Pressure Chart
Alternate term for Isobaric Chart; a weather map representing
conditions on a surface of equal atmospheric pressure. For example,
a 500 mb chart will display conditions at the level of the atmosphere at
which the atmospheric pressure is 500 mb. The height above sea level at
which the pressure is that particular value may vary from one location
to another at any given time, and also varies with time at any one
location, so it does not represent a surface of constant altitude/height
(i.e., the 500 mb level may be at a different height above sea level
over Dallas than over New York at a given time, and may also be at a
different height over Dallas from one day to the next).
CONT
Continue/Continuously
Contents
In hydrologic terms, the volume of water in a reservoir. Unless
otherwise indicated reservoir content is computed on the basis of a
level pool and does not include bank storage.
Continental Air Mass
A dry air mass originating over a large land area. Contrast with
tropical air mass.
Continental Shelf
The zone bordering a continent and extending to a depth, usually around
100 FM, from which there is a steep descent toward greater depth.
Continuum Storm (CTM)
In solar-terrestrial terms, general term for solar noise lasting for
hours and sometimes days.
Control Points
In hydrologic terms, small monuments securely embedded in the surface of
the dam. Any movement of the monument indicates a movement in the dam
itself. Movements in the dam are detected by comparing control points
location to location of fixed monuments located off the dam using
accurate survey techniques.
CONTS
continues
CONUS
Continental United States
Convection
Generally, transport of heat and moisture by the movement of a fluid.
In meteorology, the term is used specifically to describe vertical
transport of heat and moisture in the atmosphere, especially by updrafts
and downdrafts in an unstable atmosphere. The terms "convection" and
"thunderstorms" often are used interchangeably, although thunderstorms
are only one form of convection. Cbs, towering cumulus clouds, and
ACCAS clouds all are visible forms of convection. However, convection
is not always made visible by clouds. Convection which occurs without
cloud formation is called dry convection, while the visible convection
processes referred to above are forms of moist convection.
Convective Boundary Layer
The unstable boundary layer that forms at the surface and grows upward
through the day as the ground is heated by the sun and convective
currents transfer heat upwards into the atmosphere.
Convective Clouds
The vertically developed family of clouds are cumulus and cumulonimbus.
The height of their bases range from as low as 1,000 feet to a bit more
than 10,000 feet. Clouds with extensive vertical development are
positive indications of unstable air. Strong upward currents in
vertically developed clouds can carry high concentrations of supercooled
water to high levels where temperatures are quite cold. Upper portions
of these clouds may be composed of water and ice.
Convective Condensation Level
(abbrev. 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 Inhibition
(CIN or B-) - A numerical measure of the strength of "capping,"
typically used to assess thunderstorm potential. Specifically, it
represents the cumulative effect of atmospheric layers the are warmer
than the parcel moving vertically along the adiabat. Low level parcel
ascent is often inhibited by such stable layers near the surface. If
natural processes fail to destabilize the lower levels, an input of
energy from forced lift (a front, an upper level shortwave, etc.) will
be required to move the negatively buoyant air parcels to the point
where they will rise freely. Since CIN is proportional to the amount of
kinetic energy that a parcel loses to buoyancy while it is colder than
the surrounding environment, it contributes to the downward momentum.
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. The terms
approaching, slight risk, moderate risk, and high risk are used to
describe severe thunderstorm potential. Local versions sometimes are
prepared by local NWS offices.
Convective Overdevelopment
Convection that covers the sky with clouds, thereby cutting off the
sunshine that produces convection.
Convective Temperature
The approximate temperature that the air near the ground must warm to
in order for surface-based convection to develop, based on analysis of
a sounding.
Calculation of the convective temperature involves many assumptions,
such that thunderstorms sometimes develop well before or well after
the convective temperature is reached (or may not develop at all).
However, in some cases the convective temperature is a useful parameter
for forecasting the onset of convection.
Convergence
A contraction of a vector field; the opposite of divergence. Convergence
in a horizontal wind field indicates that more air is entering a given
area than is leaving at that level. To compensate for the resulting
"excess," vertical motion may result: upward forcing if convergence is
at low levels, or downward forcing (subsidence) if convergence is at
high levels. Upward forcing from low-level convergence increases the
potential for thunderstorm development (when other factors, such as
instability, are favorable). Compare with confluence.
Conveyance Loss
In hydrologic terms, the loss of water from a conduit due to leakage,
seepage, evaporation, or evapo-transpiration.
Cooling Degree Days
(Abbrev. CDD) - A form of Degree Day used to estimate energy requirements
for air conditioning or refrigeration. Typically, cooling degree days are
calculated as how much warmer the mean temperature at a location is than
65� F on a given day. For example, if a location experiences a
mean temperature of 75� F on a certain day, there were 10 CDD
(Cooling Degree Days) that day because 75 - 65 = 10.
Cooperative Observer
An individual (or institution) who takes precipitation and temperature
observations-and in some cases other observations such as river stage,
soil temperature, and evaporation-at or near their home, or place of
business. Many observers transmit their reports by touch-tone telephone
to an NWS computer, and nearly all observers mail monthly reports to
the National Climatic Data Center to be archived and published.
Coordinated Universal Time (UTC)
By international agreement, the local time at the prime meridian, which
passes through Greenwich, England. Prior to 1972, this time was called
Greenwich Mean Time (GMT) but is now referred to as Coordinated
Universal Time or Universal Time Coordinated (UTC). It is a coordinated
time scale, maintained by the Bureau International des Poids et Mesures
(BIPM). It is also known a "Z time" or "Zulu Time".
More about UTC, and a table to convert UTC to your local time is posted
at:
http://www.srh.noaa.gov/jetstream/remote/radarfaq.htm#utc
COR
Correction
Core Punch
[Slang], a penetration by a vehicle into the heavy precipitation core of
a thunderstorm. Core punching is not a recommended procedure for storm
spotting.
Coriolis Force
A fictitious force used to account for the apparent deflection of a body
in motion with respect to the earth, as seen by an observer on the earth.
The deflection (to the right in the Northern Hemisphere) is caused by the
rotation of the earth.
Corn Snow Ice
In hydrologic terms, rotten granular ice.
Corner Effects
A small-scale convergence effect that can be quite severe. It occurs
around steep islands and headlands.
Corona
1. The outermost layer of the solar atmosphere, characterized by low
densities (< 1.0x109/cc) and high temperatures (> 1.0x106 K).
2. In solar-terrestrial terms, a white or colored circle or set of
concentric circles of light of small radius seen around a luminous body,
especially around the sun or moon. The color varies from blue inside to
red outside and the phenomenon is attributed to diffraction of light by
thin clouds or mist (distinguished from halo).
Coronal Hole
In solar-terrestrial terms, an extended region of the corona,
exceptionally low in density and associated with unipolar photospheric
regions.
Coronal Rain
(Abbrev. CRN) In solar-terrestrial terms, material condensing in the
corona and appearing to rain down into the chromosphere as observed at
the solar limb above strong sunspots.
Coronal Transients
In solar-terrestrial terms, a general term for short-time-scale changes
in the corona, but principally used to describe outward-moving plasma
clouds.
Cosmic Ray
An extremely energetic (relativistic) charged particle.
County Warning and Forecast Area
The group of counties for which a National Weather Service Forecast
Office is responsible for issuing warnings and weather forecasts.
County Warning Area
The group of counties for which a National Weather Service Forecast
Office is responsible for issuing warnings.
Coupled Atmosphere-Ocean Model
Same as Coupled Model; in the context of climate modeling this usually
refers to a numerical model which simulates both atmospheric and oceanic
motions and temperatures and which takes into account the effects of
each component on the other.
Coupled Model
In the context of climate modeling this usually refers to a numerical
model which simulates both atmospheric and oceanic motions and
temperatures and which takes into account the effects of each component
on the other.
CPC
Climate Prediction Center
Creek
A small stream of water which serves as the natural drainage course for
a drainage basin of nominal, or small size. The term is a relative one
as to size, some creeks in the humid section would be called rivers if
they occurred in the arid portion.
Crepuscular Rays
The alternating bands of light and dark (rays and shadows) seen at the
earth's surface when the sun shines through clouds.
Crest
Highest point in a wave.
In hydrologic terms,
(1) The highest stage or level of a flood wave as it passes a point.
(2) The top of a dam, dike, spillway, or weir, to which water must rise
before passing over the structure.
Crest Gage
A gage used to obtain a record of flood crests at sites where recording
gages are installed.
Crest Width
In hydrologic terms, the thickness or width of a dam at the level of the
crest (top) of the dam. The term "thickness" is used for gravity and
arch dams and "width" for other types of dams.
Critical Depth
In hydrologic terms, The depth of water flowing in an open channel or
conduit, partially filled, corresponding to one of the recognized
critical velocities.
Critical Flow
In hydrologic terms, a condition of flow where the mean velocity is at
one of the critical values; ordinarily at Belanger's critical depth and
velocity. Another important usage is in reference to the Reynolds'
critical velocities which define the point at which the flow changes
from streamline or nonturbulent to turbulent flow.
Critical Rainfall Probability
(Abbrev. CRP) - In hydrologic terms, the Probability that the actual
precipitation during a rainfall event has exceeded or will exceed the
flash flood guidance value.
CRN
Coronal Rain - In solar-terrestrial terms, material condensing in the
corona and appearing to rain down into the chromosphere as observed at
the solar limb above strong sunspots.
Crochet
In solar-terrestrial terms, a sudden deviation in the sunlit geomagnetic
field (H component; see geomagnetic elements) associated with large
solar flare X-ray emission.
Crop Moisture Index
In 1968, Palmer developed the index to assess short-term crop water
conditions and needs across major crop-producing regions. This index
is a useful tool in forecasting short-term drought conditions.
Cross-Valley Wind System
A thermally driven wind that blows during daytime across the axis of a
valley toward the heated sidewall.
Crown Fire
A fire where flames travel from tree to tree at the level of the tree's
crown or top.
Crowning
Movement of a fire from the understory into the crown of a forest canopy.
CRP
Critical Rainfall Probability - in hydrologic terms, the probability that
a given rainfall will cause a river, or stream to rise above flood stage.
CRS
Console Replacement System for NOAA Weather Radio.
Cryology
The science of the physical aspects of snow, ice, hail, and sleet and
other forms of water produced by temperatures below 0� Celsius.
CSDRBL
Considerable
CSI
Conditional Symmetric Instability
CST
Central Standard Time
CSTL
coastal
CTY
city
CU
Cumulus clouds - Detached clouds, generally dense and with sharp
outlines, showing vertical development in the form of domes, mounds,
or towers. Tops normally are rounded while bases are more horizontal.
See Cb, towering cumulus.
Cubic Feet per Second
(Abbrev. CFP) - In hydrologic terms, a unit expressing rates of
discharge. One cubic foot per second is equal to the discharge through
a rectangular cross section, 1 foot wide by 1 foot deep, flowing at an
average velocity of 1 foot per second. It is also approximately 7.48
gallons per second.
CUFRA
Cumulus Fractus
Cumuliform
Descriptive of all clouds with vertical development in the form of
rising mounds, domes, or towers.
Cumuliform Anvil
A thunderstorm anvil with visual characteristics resembling cumulus-type
clouds (rather than the more typical fibrous appearance associated with
cirrus). A cumuliform anvil arises from rapid spreading of a
thunderstorm updraft, and thus implies a very strong updraft. See
anvil rollover, knuckles, mushroom.
Cumulus
(Abbrev. CU) - detached clouds, generally dense and with sharp outlines,
showing vertical development in the form of domes, mounds, or towers.
Tops normally are rounded while bases are more horizontal. See Cb,
towering cumulus.
Cumulus Buildups
Clouds which develop vertically due to unstable air. Characterized by
their cauliflower-like or tower-like appearance of moderately large size.
Cumulus Congestus
A large, towering cumulus cloud with great vertical development, usually
with a cauliflower-like appearance, but lacking the characteristic anvil
of a cumulonimbus.
Current
A horizontal movement of water. Currents may be classified as tidal and
nontidal. Tidal currents are caused by gravitational interactions
between the sun, moon, and earth and are a part of the same general
movement of the sea that is manifested in the vertical rise and fall,
called TIDE. Tidal currents are periodic with a net velocity of zero
over the tidal cycle. Nontidal currents include the permanent currents
in the general circulatory systems of the sea as well as temporary
currents arising from more pronounced meteorological variability. The
SET of a current is the direction toward which it flows; the DRIFT is
its speed.
Current Meter
In hydrologic terms, device used to measure the water velocity or current
in a river.
Curtain Drain
In hydrologic terms, a drain constructed at the upper end of the area to
be drained, to intercept surface or ground water flowing toward the
protected area from higher ground, and carry it away from the area. Also
called an Intercepting Drain.
Cutoff
In hydrologic terms, from passing through a dam's foundation material.
An impervious construction or material which reduces seepage or prevents
it.
Cutoff Low
A closed upper-level low which has become completely displaced (cut off)
from 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 (i.e., retrogression).
"Cutoff low" and "closed low" often are used interchangeably to describe
low pressure centers aloft. However, not all closed lows are completely
removed from the influence of the basic westerlies. Therefore, the
recommended usage of the terms is to reserve the use of "cutoff low" only
to those closed lows which clearly are detached completely from the
westerlies.
CVR
Cover
CWA
County Warning Area
CWFA
County Warning and Forecast Area
CYC
Cyclone- A large-scale circulation of winds around a central region of
low atmospheric pressure, counterclockwise in the Northern Hemisphere,
clockwise in the Southern Hemisphere.
CYCLGN
Cyclogenesis - The formation or intensification of a cyclone or
low-pressure storm system.
Cyclic Storm
A thunderstorm that undergoes cycles of intensification and weakening
(pulses) while maintaining its individuality. Cyclic supercells are
capable of producing multiple tornadoes (i.e., a tornado family)
and/or several bursts of severe weather.
Cyclogenesis
(Abbrev. CYCLGN) - The formation or intensification of a cyclone or
low-pressure storm system.
Cyclone
(abbrev. CYC) - A large-scale circulation of winds around a central
region of low atmospheric pressure, counterclockwise in the Northern
Hemisphere, clockwise in the Southern Hemisphere.
Cyclonic Circulation
Circulation (or rotation) which is in the same sense as the Earth's
rotation, i.e., counterclockwise (in the Northern Hemisphere) as would
be seen from above. Nearly all mesocyclones and strong or violent
tornadoes exhibit cyclonic rotation, but some smaller vortices, such
as gustnadoes, occasionally rotate anticyclonically (clockwise).
Compare with anticyclonic rotation.
--- SBBSecho 3.07-Win32
* Origin: The Thunderbolt BBS - tbolt.synchro.net (801:1/2)
� Synchronet � Temple of Doom BBS - tod.eothnet.com
