It will easily be the most widespread rain since mid-December, when 20 to 40mm affected a large area of South Australia, Tasmania, Victoria and southern New South Wales.

And the timing is almost as good as it gets with many grain farmers in the process of sowing, according to FarmOnline Weather.

Good rainfall around Anzac Day provides the best timing for kicking off the southern wheatbelt winter cropping season - providing the critical 'break in the season'.

For some, it will be the most rain since last winter or beyond due to warm, moist air from the northwest linking up with cold, unstable air from the south.

Strong cold fronts every day-or-two will mean some rain is likely each day for at least five-days running.

For many in the southern Murray-Darling, this will be very welcome rain.

Mannum, Lameroo, Waikerie, Loxton, Murrayville, Wentworth, Finley and Kyabram have all had one of their driest starts to the year on record with less than 10mm being recorded.

The rain will spread across SA on Thursday and across Tasmania, Victoria and southern NSW on Friday as a northwest cloudband links up with a cold front.

Further cold fronts will help rain amounts total 10 to 20mm during the next five-or-six days.

Falls of more than 50mm are possible near the coasts and ranges.

In Victoria, Bureau of Meteorology senior forecaster Phil King said the first front coming in from the west was approaching Victoria's western border today and would move through the state tomorrow, bringing widespread rain and possible thunderstorms.

Ensuing fronts will force a cold snap on Sunday, with the chance of snow down to 1000 metres.