The second-warmest May on record, coupled with above-average rainfalls in the Murray-Darling Basin, have led climatologists to speculate that a drought-breaking La Nina event is still on its way.

An almost complete lack of cold southerlies, rather than extreme heat, had led to May being warm by day and night across almost the whole country, according to the National Climate Centre's Blair Trewin.

The centre was still "reasonably confident a La Nina event (linked with widespread high rainfall) would happen".

"It's not definite but it is looking quite likely," the climatologist said.

Information released by the Murray-Darling Basin Commission yesterday said rain fell across the southern part of the basin this week, with 15-70mm falling across northeast Victoria and southern NSW.

This week's rainfalls have sufficiently drenched the parched catchments to generate run-off into the system, although the commission's managing director, David Dreverman, warned that "sustained high inflows" would be required throughout winter and spring "to significantly improve water availability".

Precipitation in a different form fell over Victoria's ski fields this week, with Mt Buller receiving 20cm of snow before the official start to the ski season next weekend.

The resort received wind gusts of up to 177km/h on Tuesday, which turned into rain and snow overnight.

After clear blue skies yesterday, temperatures are forecast to remain low this weekend, with snow to fall for three days.

"Last year we had snow at Easter (but) really marginal snow on opening weekend," Mt Buller spokeswoman Amber Gardner said. "This year, we're hoping to have at least 20cm."

Patchy snow covers the NSW resorts of Thredbo and Perisher Blue. Despite the cold conditions bringing the snowfalls, mean temperatures for May were exceptionally warm.

Records were set for the combined temperatures over almost all of Victoria and Tasmania, parts of the eastern half of South Australia, most of NSW and most of Queensland.

"The only thing which is going to stop it from being the warmest May on the whole is a relatively cool month in southern WA," Dr Trewin said.

Across Australia, autumn was likely to be the sixth-warmest on record. Three significant rain events in the past six weeks indicated patterns were returning to normal, Dr Trewin said.