Daylight Saving Concludes in Australian States, Affecting Weather Data Collection

Daylight Saving Time will conclude on Sunday, April 5, in New South Wales, Victoria, the Australian Capital Territory, Tasmania, and South Australia. Clocks in these regions will revert one hour from 3:00 AM to 2:00 AM. This transition to standard time will establish new time differences across Australia and impact the collection and comparison of 9:00 AM weather observations by the Bureau of Meteorology (BoM).

On Sunday, April 5, Daylight Saving Time (DST) will end in New South Wales, Victoria, the Australian Capital Territory (ACT), Tasmania, and South Australia. At 3:00 AM on this date, clocks in these states and territories will be set back by one hour, effectively becoming 2:00 AM. This adjustment marks the return to standard time.

Regional Time Differences

Following the change, new time differences will be established across Australia.

• Perth will be two hours behind the eastern capitals (Sydney, Melbourne, Hobart, Canberra).
• Adelaide and Darwin will be 30 minutes behind the eastern capitals.

These time differences are expected to remain in place until Daylight Saving Time recommences in October.

Impact on Weather Data Collection

The conclusion of Daylight Saving Time affects the collection and comparability of weather data, particularly the 9:00 AM observations.

The Bureau of Meteorology (BoM) compiles Australian weather data based on a 24-hour weather day cycle, from 9:00 AM to 9:00 AM. Many weather stations, including remote or manually operated ones, record observations at 9:00 AM. Some stations also record data at 3:00 PM, while others record exclusively at 9:00 AM.

When Daylight Saving Time ends, the 'old' 9:00 AM observation effectively shifts to an hour later in standard time. This creates an inconsistency for comparisons of 9:00 AM readings across the month of April, as the observation time relative to solar time changes.

This shift can create statistical challenges for specific point-in-time data, such as temperature or humidity readings at 9:00 AM. The period between 8:00 AM and 9:00 AM standard time often experiences a rapid rise in air temperature, which accentuates the impact of comparing data when 9:00 AM effectively represents two different times during the month.

Daily maximum and minimum temperature data are not affected by this time change. These values represent the highest and lowest temperatures recorded at any point within the 24-hour weather day, rather than a fixed point in time.