Air density

The mass of a cubic metre of air. This depends on the temperature and barometric pressure.

Cooling degree-day

The same as a heating degree-day, except it measures how much the temperature is above 18.3 C, and thus how much cooling (air conditioning) is required to bring the temperature down to this level.

Dew point

Temperature at which water vapour in the air would condense as fog or rain.

ET (Evapotranspiration)

A measure of the amount of evaporation and transpiration (from plants) of water vapour into the air. Will be higher at higher temperatures and/or lower humidity.

Heat index / humidex

Humidity makes it feel warmer as it inhibits the evaporation of perspiration in warm weather. The heat index is the perceived temperature, taking account of humidity.

Heating degree-day

A measure of the amount of heating required when the temperature drops below a standard value. (I use 18.3 C (65 F), which is standard.) If the temperature is one degree below 18.3 for one day, that equals one heating degree-day.

Humidity (relative)

The amount of water vapour in the air as a percentage of the maximum possible. At 100% humidity, the water vapour will condense into fog or rain.

Reception

The percentage of data packets received by the VantagePro2 console in each 15 minute period. Ideally this should always be 100% but due to unknown causes, sometimes the console loses the connection, resulting in gaps in the data.

Solar radiation

The amount of energy (in watts per square metre) being received from the sun.

UV index

A measure of the intensity of solar ultraviolet radiation, used mainly for determining how quickly exposed skin will burn in the sun.

Wind chill

When it's windy, it feels colder. Wind chill is the temperature we feel, rather than the actual air temperature.