Weather Glossary – C


CAA – Cold Air Advection. The movement of colder air toward a fixed point on the earth’s surface.

CALM – the absence of apparent motion in the air.

CAP – Temperature inversion which prevents convection from occurring.

CAT – A category. Usually refers to a category of precipitation given by the forecast models.

CEILING – The height of the lowest layer of clouds, when the sky is broken or overcast.

CELSIUS – a temperature scale in which zero is the freezing point of water and one hundred is the boiling point.

CHANCE (CHC) – A 30, 40 or 50 percent chance of occurrence of measurable precipitation.

CHINOOK- A warm, dry wind that blows along the east slopes of the northern Rocky Mountains.

CIRRIFORM – High altitude ice clouds with a very thin wispy appearance.

CIRROCUMULUS – Cirrus clouds with vertical development.

CIRROSTRATUS – Cirrus clouds with a flat sheetlike appearance.

CIRRUS (CI) – High clouds, usually above 18,000 feet, composed of ice crystals.

CLASSIC EVENT– Having all the ingredients for a specific type of weather (i.e. classic severe weather event, classic Nor’easter)

CLEAR – Sky condition of less than 1/10 cloud coverage.

CLIMATE – The historical record of average daily and seasonal weather events.

CLOSED LOW (CUT OFF LOW) – A low pressure center having a closed circulation, which is used in reference to systems in the upper levels of the atmosphere. Closed lows that become cut off from the main flow pattern are called cut-off lows.

CLOUD CONDENSATION NUCLEI – small particles in the air on which water vapor condenses and forms cloud droplets.

CLOUDY– the state of the sky when 9/10ths or more of the sky is covered by clouds.

COASTAL FLOODING – Inundation of coastal areas from waves and storm surge. 

COLD CORE HIGH– A dome of cold surface high pressure that originates from the high latitudes.

COLD CORE LOW– A low pressure which has the coldest temperatures located near its center. A cold core low is deep and is often associated with the polar jet stream. Mid-latitude cyclones are cold core lows. 

COLD FRONT – The boundary between a cold air mass that is advancing and a relatively warmer airmass. Generally characterized by steady precipitation followed by showery precipitation.

CONDENSATION – The process of gas changing to liquid. The process by which water vapor changes into water droplets and clouds.

CONDENSATION PRESSURE DEFICIT (COND PRES DEF)– On an isentropic chart (a layer of constant potential temperature), condensation pressure deficit represents the amount of lift, expressed in millibars, needed to saturate an air parcel.

CONDUCTION – the transfer of heat between bodies that are in contact.

CONFLUENCE– A 2-D process in which airstreams move toward each other at some angle.

CONQ– Converging Q vectors. Indicates air will rises due to low level warm air advection and/or upper level divergence

CONSIDERABLE CLOUDINESS – Between 7/10 and 8/10 cloud cover.

CONTINENTAL AIR MASS – A dry air mass originating over a large land area.

CONVECTION (CNVTN) – the transfer of heat within a gas or liquid by their movement.

CONVECTIVE INSTABILITY– Instability caused by very dry air advecting in the mid-levels of the troposphere over a warm and moist lower troposphere. Dynamic lifting causes the mid-levels to cool at a greater rate than the lower troposphere.

CONVERGENCE– A 1-D process in which higher momentum air moves into lower momentum air.

CORIOLIS FORCE – An apparent force caused by the rotation of the earth. In the Northern Hemisphere winds are deflected to the right, and in the Southern Hemisphere to the left.

CORONA – a disk of light surrounding the sun or moon; this is a result of the diffraction of light by small water droplets.

COUNTY WARNING AREA (CWA) – The area of responsibility that each National Weather Service office has for its warnings and forecasts.

CUMULONIMBUS – A vertically developed cumulus cloud, often capped by an anvil shaped cloud. Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail or gusty winds.

CUMULUS CLOUD (CU) – A cloud in the shape of individual detached domes, with a flat base and a bulging upper portion resembling cauliflower.

CWA– County Warning Area

CYCLONE – An area of low pressure around which winds blow counterclockwise in the Northern Hemisphere. Also the term used for a hurricane in the Indian Ocean and in the Western Pacific Ocean.