Snow may fall in the southern parts of the South Island when the first really cold south-westerly blast of the winter sweeps up the mainland on Sunday and Monday, MetService says.

The front will arrive over southern New Zealand late on Sunday and spread across much of the South Island on Monday.

Farmers are being warned to move stock to shelter as snow may fall to a few hundred metres above sea level in Fiordland, Southland and Otago.

"This will be the first decent shot of cold air out of the Southern Ocean for some months," meteorologist Daniel Corbett says.

"The good thing about this cold outbreak is that it's over fairly quickly," he says.

"The southwest winds over the country should die away during Tuesday, which means frosts are likely that night."

More settled and less cold air will spread in by midweek.

The cold blast is expected to be welcomed by skifields, which have been busy preparing facilities during a warm summer and autumn in the southern South Island.