Daylight Saving Time and weather observations

Daylight Saving Time (DST) has been implemented within Australia in various forms since the early 1900s. Since it began, the times at which weather observations were made by the Bureau of Meteorology during the period of DST also underwent a number of changes in practice. In different years an observation may have been made based either on local clock time, or according to local standard time ignoring DST. The impact of these changes is probably most significant on the nominal 9am data, particularly temperature and humidity observations.

The following sections provide more detailed information:

Glossary

UTC - Coordinated Universal TimeCoordinated Universal Time is the worldwide standard for time and date, and is based on an atomic clock. For most practical purposes UTC has superceded (but is similar to) Universal Time (UT1) which is derived from astronomical observations, as was the previous standard Greenwich Mean Time (GMT). Current UTC time can be retrieved from the BIPM UTC/TAI Time Server maintained by the Bureau International des Poids et Mesures.LST - Local Standard TimeThe globe is divided into Standard time zones and Local Standard Time is the time specified for each zone. This is usually done in terms of hours ahead or behind UTC. The LST zones in Australia are as follows:

EST - Australian Eastern Standard Time (+10 UTC) in Qld, NSW, Vic and Tas

CST - Australian Central Standard Time (+9.5 UTC) in NT and SA

WST - Australian Western Standard Time (+8 UTC) in WA

DST - Daylight Saving TimeAlso known as summer time, Daylight Saving Time occurs when the time on local clocks is advanced forward by one hour at the beginning of the defined period of DST, and returned back by one hour at the end of DST. The exact dates between which DST is to apply can be obtained from the relevant Australian State governments. Within Australia DST across the time zones is generally denoted by:

EDT - Australian Eastern Daylight Time

CDT - Australian Central Daylight Time

Local TimeNormally this is the same as Local Standard Time, but in periods of Daylight Saving an hour is added to the local clock, making Local Time an hour ahead of Local Standard Time (ie Local time = DST).