It's going to be dry across most of Australia for the rest of this week, continuing a trend that many have become accustomed to during 2018.

The lack of rainfall across mainland Australia this week is being caused by a couple of factors.

Firstly, an index called the Southern Annular Mode (SAM) is currently in a positive phase, which means that a belt of westerly winds surround Antarctica is displaced to the south. During a positive phase of the SAM, cold fronts tend to be less active over southern Australia.

In addition to the SAM, most of Australia is currently surrounded by water that's cooler than usual for this time of year, particularly off the nation's southern, western and northwestern coastlines. Cooler sea surface temperatures suppress evaporation, which leads to less atmospheric moisture and a reduction in rainfall.

During early spring, much of the rain in southern and central Australia occurs when moisture from the Indian Ocean interacts with cold fronts pushing north over Australia. Unfortunately, these two key ingredients are lacking this week and thus so is the rain.

This week's dry weather comes after a notably dry start to 2018 across much of Australia, particularly in the southeast.

The Murray Darling Basin registered its driest January to July period since 1965, while southern Australia registered its second driest autumn in more than a century and Australia as a whole experienced its 14th driest winter on record.

The latest seasonal outlook issued by the Bureau of Meteorology at the end of August suggests that drier and warmer than usual weather is to continue for most of Australia during spring.