MetService meteorologist Stephen Glassey said a cold front was expected to move over the South Island later on Saturday and continue into Sunday, before moving over the North Island.
Auckland is set to remain cool, with highs of just 16-17C for the next five days, and forecast to drop down to 14C next Tuesday.
Temperatures across the South Island are expected to fall to single figures next week, with Christchurch down to 9C on Monday and 10C on Tuesday with frosts.
It follows a front that is expected to cross the country tonight and become slow-moving, bringing significant heavy rainfall to the West Coast, Fiordland and the headwaters of the Otago lakes and rivers from tomorrow to early Saturday.
The drop in temperature on Saturday night was expected to bring snow to much of the southern region, he said.
"We're forecasting snow down to about 300m in Southland and the Clutha area, and certainly there will be some for parts of Otago.
"The flow does look quite westerly following this front, so it may be that lots of Otago is sheltered from that flow.
"It doesn't look like much will get into Dunedin - possibly just a dusting.
"We'll just have to wait until we get a bit closer to the time, to be sure about that.
"Certainly the skifields will see some fresh snow."
He said there were indications that the colder-than-average temperatures would continue across the country next week, so the snow might continue into Monday and Tuesday.
Despite the forecast, he said it was still too early to say with certainty where or how much snow would fall.
He said residents should keep up-to-date with the weather forecast.
Additional reporting John Lewis ODT
