• Weather Glossary (C)

    From Daryl Stout@57:57/10 to All on Tue Oct 13 00:07:32 2020
    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 3.11-Win32
    * Origin: The Thunderbolt BBS - tbolt.synchro.net (57:57/10)