Mother Nature is about to flex her muscles with predictions the worst storm of the year about to hit the South Island

Warnings are out that major snowfalls could cut off Arthur's Pass and other alpine passes from Sunday onwards.

Blue Skies Weather forecaster Tony Trewinnard says he's not one to sensationalise the weather but travellers will have to be careful.

He says there will be big snowfalls in Southland and most of Otago - possibly down to low levels - from Sunday to Tuesday.

Trewinnard says this is probably the biggest weather event of the year, and if it had landed in winter could have shut the South Island down.