Since 16 December 2019, the heat had been building up in most of Australia. The plot below is the daily maximum temperatures from 18 Dec to 20 Dec. It is shown that temperatures exceed 40oC in many stations especially over southeast of Australia. On 19 Dec, Nullarbor station in South Australia records 49.9oC.
Figure 1 Daily maximum temperatures from 18 Dec to 20 Dec in Australia
The severe heatwave condition is estimated to persist over most of Australia apart from the western and southern parts for the following two days as shown in the plots below.
Figure 2 Forecast for daily maximum temperature for 22 Dec and 23 Dec in Australia