Glossary

Refers to extensive cooling of the central and eastern tropical Pacific Ocean and neighbouring countries. In Australia (particularly eastern Australia), wet weather is more likely during La Niña events.

The delay in the time of occurrence of high and low water due to changes in relative position of the Moon and the Sun. See also lunitidal interval.

Breeze blowing from land towards the sea, due to the relative warmth of the sea.

The rate of change of temperature with height in the atmosphere.

If hail larger than 2 cm across is expected, we use the words ‘large hail' in our forecast.

The energy absorbed or released during a change of state. Evaporation, melting and sublimation (a change from solid to gas) absorb heat from the surrounding air as energy is needed to weaken the individual hydrogen bonds between the water molecules. Condensation, freezing and deposition (gas to solid) release the latent heat, thus adding heat to the surrounding air.

A geographic coordinate that specifies the north-south position of a point on the earth’s surface. It is measured as the angular distance, subtended at the earth’s centre, along a meridian from a point on the earth to the equator. The equator is designated as zero degrees and the poles as 90 degrees.

The side of an obstacle that is furthest away from the wind.

A more-or-less isolated cloud, downwind of a barrier, resembling a smooth lens with sharp outlines. They mostly occur in mountain waves, and thus indicate possible severe turbulence and icing.

The height at which a parcel of saturated air becomes warmer than the surrounding air and thus begins to rise freely until it reaches its equilibrium level.

The height at which a parcel of moist air becomes saturated when it is cooled by adiabatic lifting.

Wind speeds of 19 km/h or less.

The bright flash of light accompanying an electrical discharge:

• within a cloud
• between clouds
• from clouds to the ground
• from the cloud top into the surrounding atmosphere.

Possible', 'chance' and 'risk'
May be used interchangeably for location forecasts. Indicates a weather element is expected in the area but there is only a chance of it happening in that specific location. This is due to the random nature of showers and thunderstorms – they can be hit and miss. 'Risk' is generally used about thunderstorms.

'Slight', 'medium', 'high', 'very high' chance
Indicates whether a location is likely to receive a measurable amount of rainfall (>0.2 mm) during the day.

The globe is divided into standard time zones. Local standard time (LST) is the time specified for each zone. This is expressed in terms of hours ahead or behind coordinated universal time (UTC). The LST zones in Australia are:

• EST – Australian Eastern Standard Time (+10 UTC) in Queensland, New South Wales, Victoria and Tasmania
• CST – Australian Central Standard Time (+9.5 UTC) in Northern Territory and South Australia
• WST – Australian Western Standard Time (+8 UTC) in Western Australia.

Areas such as bays, harbours and inland waters on which frequent boating activity occurs.

A geographic coordinate that specifies the east-west position of a point on the earth’s surface. It is measured as an angle in reference to the Prime Meridian, which is designated as zero degrees longitude.

In the southern hemisphere, areas north of about 30° latitude.

For Australia, the low latitudes are north of a line from halfway between Perth and Geraldton in Western Australia to Bourke in New South Wales. This part of Australia generally has a subtropical to tropical climate.

A transient strong wind concentrated in relatively narrow bands near the earth’s surface.

Atmospheric circulations of low pressure that rotate clockwise in the southern hemisphere. Low pressure systems generally bring stronger winds, unsettled conditions, clouds and rain.

The lowest of the low waters of any specified tidal day due to the declinational effects of the Moon and Sun.

The lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. Increasingly used as chart datum, for example, for all new Australian charts. Also referred to as LAT.

A tidal constituent whose origins are a combination of lunar and solar – that is, by coincidence, there are identical force frequencies stemming from both sources.

The average duration of time between the high point of the Moon to the next high tide at any given location. Also called high water interval.