During the past week, a series of fronts and troughs traversed the Great Australian Bight, accompanied by intense masses of cold air that brought extreme cold throughout the southern region of the country. 

Subzero temperatures (shades of pink on the map below) were observed over New South Wales, including Canberra, as well as in Victoria, southern South Australia, Western Australia, and far south Queensland. 

Image: Lowest Minimum Temperature (°C) during the 7 days ending July 21st, 2023. Source: BoM

It's not surprising to talk about cold weather during this time of year. However, what has drawn attention is that the mornings have been unusually colder than normal in certain regions.

Notably, central and southern Western Australia, southeastern South Australia, western Victoria, and southwestern New South Wales experienced minimum temperatures that were up to 6°C lower than the average for this time of year (shades of green on the map below).

Image: Minimum Temperature Anomaly (°C) during the 7 days ending July 21st, 2023. Source: BoM

This map also indicates that while the southern regions had a week with considerably colder mornings than usual, the central and northern parts of the country experienced warmer mornings. Much of Queensland, central Western Australia, and the Northern Territory had low temperatures 4- 8°C higher than the average (shades of orange on the map above).

One of the explanations for this contrast is the negative phase of the Southern Annular Mode (SAM), which generates a strong flow of westerly winds and fronts passing through the south, while a large high-pressure system dominated much of Australia.

In the next few days, SAM is expected to enter a neutral phase, which should help bring morning temperatures closer to the average. To get information about the upcoming temperatures in your region, visit weatherzone.com.au.