Parts of southern and southeastern Australia could see their best rain in more than a year this week, but like most rain events, some places will miss out.

Cloud is building over South Australia today as a stream of tropical moisture interacts with an upper-level pool of cold air moving into the Great Australian Bight.

Image: Enhanced water vapour satellite image showing a stream of tropical moisture clashing with an injection of cold air from the south.

The cloud will cause showers and storms to spread across South Australia on Tuesday, initially in the west, before reaching central districts in the evening. These showers will be accompanied by a blustery cool change as a cold front passes over the state from west to east.

Showers and cool, blustery winds will continue to affect southern districts of South Australia between Wednesday and Friday, as a complex low pressure system develops over the Bight.

The impending spell of cold, wet and windy weather has prompted a warning to sheep graziers in seven South Australian districts, where lambs and sheep will be threatened by wintry conditions between Tuesday and Friday.

The frontal system and complex low will also cause rain to spread across large areas of NSW, Victoria, Tasmania and southern Queensland between Wednesday and Saturday. This rain will be accompanied by severe thunderstorms in some areas.

Widespread rainfall totals of 10-20mm are likely between Tuesday and Saturday, while some areas could see more than 50mm, particularly about the Victorian ranges and with intense thunderstorms. Most places will see this rain falling in just one or two days.

Forecast models suggest that parts of South Australia's West Coast, northern Tasmania, central and northern Victoria and southern NSW could see their best rain in more than a year during the next few days.

The impending rain will be welcome in southern and southeastern Australia. Both Adelaide and Melbourne just experienced their driest start to a year on record.