C
Land where water, especially rainfall, drains into storage, such as a lake, pond or basin.
Instrument for estimating cloud amount and height.
Temperature scale (range of values) where water freezes at 0 °C and boils at 100 °C at sea level.
Describes the likelihood of receiving a measurable amount of rain (>0.2 mm) during the day. For example, if the chance of rain for Mildura is 30%, rain will be measured in the Mildura rain gauge on 3 out of 10 days with similar weather conditions. Where there is a 30% chance of any rain, there is a 70% chance of no rain. By similar weather conditions we mean similar levels of moisture, temperatures, air movement and so on.
Change in weather indicated by a transition between 2 air masses over a short time. This is usually when a cooler air mass replaces a warmer one. A change may bring a rapid change in wind direction and sometimes rain. This is usually from a warmer north to northwesterly wind to a cooler southeast to southwesterly one.
Artificial or constructed waterway designed to carry water.
Wispy, feathery-looking cloud formed high in the atmosphere and made of ice crystals.
Free from cloud, fog, mist or haze.
Weather or atmospheric conditions experienced or forecast in an area, averaged over a long period. This can be a few weeks to millions of years.
Scientific study of climate. Also known as climate science.
Mass of water droplets or ice crystals, caused by water vapour in the atmosphere condensing or freezing.
Degree to which cloud covers the sky. Forecasting terms relating to cloud cover:
- Clear
- Sunny
- Partly cloudy
- Cloudy
- Overcast.
Forecasts of cloud cover normally give the main state if no significant variations are expected. A clear day, for example, may 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, the forecast will usually indicate a distinct trend, for example, becoming sunny or cloud increasing.
More cloud than clear sky.
Cloud expected to cover about 65–100% of the sky for most the day. For example, during the day the sun would be obscured by cloud for lengthy periods.
Leading edge of a relatively cold air mass moving into a region of warmer air.
Combined height of the sea and the swell that mariners experience on open waters. Refers to the average wave height of the highest third of the waves.
Also known as significant wave height and total wave height.
Change from a gas to a liquid. This process is also called condensation – a term that is also used to describe the liquid droplets formed.
Line joining points of equal value on a surface.
Process generally linked with warm rising air and the formation of cloud. For example, on hot days when the land and air above heats up, that air begins to rise. As the air rises it cools. If it cools enough, the water vapour in it condenses and forms cloud (sometimes called convective cloud). If a lot of air warms and rises, a thunderstorm may develop.
When air flows into a region.
Main standard by which the world regulates clocks and time. It's also known as Greenwich Mean Time. In some forecasts and reports it is signified by the letter Z.
Describes how the Earth's rotation deflects large moving masses of air or water. In the southern hemisphere, these masses appear to turn to the left (and to the right in the northern hemisphere). The Coriolis effect influences large-scale oceanic and atmospheric circulations, including weather patterns, cyclone formation, tidal direction and currents. It's greatest at the poles and non-existent at the equator.
Abbreviation of the Commonwealth Scientific and Industrial Research Organisation, Australia’s science agency.
Very tall, puffy, heaped, dark cloud that often has a dark base and brings rain. Some have a distinctive anvil-shaped top.
Also known as thunderstorm cloud, producing thunder and lightning.
Cloud that usually has a flat base and clumpy, cauliflower-shaped upper surface. It forms in the low levels of the atmosphere.
Rapid development or increasing intensity of a low pressure system.
Often called low pressure systems, cyclones are atmospheric circulations that rotate clockwise in the southern hemisphere, and anticlockwise in the northern hemisphere. They are areas of lower air pressure that may bring stronger winds, unsettled conditions, cloudiness and rain. See also tropical cyclone.