C
The terms and definitions found in the glossary relate to the science of meteorology.
For descriptions and definitions of words used in the Bureau's forecasts and warnings, please refer to Weather Words.
- Carbon dioxide
- A gas (CO2) present in the atmosphere which plays an important role in the greenhouse effect.
- Celsius temperature scale
- Thermodynamic scale of temperature. Temperature in degrees Celsius can be obtained from value in degrees Fahrenheit by the following formula:
C = (F - 32) x 5/9 - Chance of any rain
Chance of rain describes the likelihood of receiving a measurable amount of rain (>0.2mm) during the day at that location. For example, if the chance of rain for Mildura is 30%, it means that on 3 out of 10 days with similar weather conditions rainfall will be measured in the Mildura rain gauge. Where there may be a 30% chance of any rainfall, there is also a 70% chance of not receiving any rainfall at all.
Slight chance, Medium chance, High chance, Very high chance
- Slight chance is used when the likelihood is between 15% and 34%.
- Medium chance is used when the likelihood is between 35% and 64%.
- High chance is used when the likelihood is between 65% and 84%.
- Very high chance is used when the likelihood is 85% or higher.
For example, if the forecast is "Medium chance of showers" there is between a 35% and 64% chance of showers resulting in at least 0.2 mm of rainfall during the day.
- Chlorofluorocarbons
- Chemicals that release chlorine atoms that destroy ozone high in the atmosphere. An animation of the process may be viewed by clicking here.
- Cirrus cloud
- High cloud, delicate, hair-like and feathery looking.
- Climate
- The atmospheric conditions for a long period of time, and generally refers to the normal or mean course of the weather. Includes the future expectation of long term weather, in the order of weeks, months or years ahead.
Click here for more information. - Cloud
- Mass of water droplets or ice crystals caused by water vapor in the atmosphere condensing or freezing. See Fig. 1 below for an animation and explanation of how clouds form over mountains.
Fig. 1
As air flows against and over a mountain range, it cools as it rises. The water vapour in the rising air condenses into droplets and forms clouds. When the droplets are large enough they may fall as rain.
Most clouds are formed by the ascent and consequent cooling of air to the point of saturation. When the air is saturated, further cooling results in the appearance of liquid water particles and/or tiny ice crystals.
See the Clouds page for more detail and the four ways in which moist air can be lifted to form clouds. - Cloud cover
- Forecasting terms:
- Clear: Free from cloud, fog, mist or dust haze.
- Sunny: Little chance of the sun being obscured by cloud. Note: High level cirrus clouds are often thin and wispy, allowing a considerable amount of sunlight to penetrate them, sufficient to produce shadows. In this case the day could be termed 'sunny' even though more than half the sky may be covered in cirrus cloud.
- Cloudy: Predominantly more cloud than clear sky for example, during the day the sun would be obscured by cloud for substantial periods of time.
- Overcast: Sky completely covered with cloud.
Forecasts of cloud cover normally give an average, if no significant variations are expected. A clear day, for example, may at some times see a few cloud patches.
Forecasters expecting significant variations in cloud amount may use such terms as sunny periods, sunny breaks, cloudy periods, cloudy at times, mostly/mainly sunny, mostly/mainly cloudy.
If expecting a major change in cloud cover, they usually indicate a distinct trend, e.g. becoming sunny or cloud increasing. - Cold Fronts
- See Front (Cold).
- Combined Sea and Swell
- Also known as total wave height, or significant wave height. Combined sea and swell describes the combined height of the sea and the swell that mariners experience on open waters. The height of the Combined sea and swell refers to the average wave height of the highest one third of the waves. A lookup table has been developed to outline how the Combined sea and swell is calculated.
See also Sea and Swell - Condense
- Change from a gas to a liquid.
- Contract
- To reduce in size.
- Convection
- The process generally associated with warm rising air and the formation of cloud. Local breezes, wind and thunderstorms are a result of convection in the atmosphere.
- Cumulonimbus cloud
- Heavy, puffy, heaped, dark cloud of great vertical depth, often bringing rain. Some have a distinctive anvil shaped head.
- Cumulus
- Clouds with a woolly, heaped appearance that often produce rain.
- Cyclogenesis
- The rapid development of a low or intensification of a pre-existing one.
- Cyclone
- Atmospheric circulations that rotate clockwise in the southern hemisphere, and anti-clockwise in the northern hemisphere. Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall.
See also Tropical cyclones under for more information.