A chilly band of weather drags us back into winter this weekend with snowfall forecast to sea-level in the south and temperatures plunging.

MetService meteorologist Ciaran Doolin said a serious of cold fronts is moving up the South Island today.

They're already hitting southern areas and will reach Nelson by evening.
Heavy snow warnings are in place for Southland, Clutha, southern Fiordland, Otago and Banks Peninsula.

Right now areas down to 300 metres above sea level in Southland and 500 metres in Otago are getting a dusting but it could reach sea-level this evening in those areas, Mr Doolin said.

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Above the Canterbury Plains snow will fall down to about 400 metres.

Mr Doolin said temperatures would also fall with the "usual suspects" hit the hardest.

Inland areas around Mt Cook, Lake Pukaki and Twizel will shiver through a -6C night and some parts of Central Otago, around Cromwell, Clyde and Alexandra, will drop to about -4C. The North Island isn't so bad today.

"We've got a low off to the north east of the country," Mr Doolin said.

"That's bringing a fair bit of [rain] to parts of Northland, northern Auckland and the Coromandel."

A heavy rain watch is in place for northern Auckland and Great Barrier Island and there is a heavy rain warning for Northland.

"It's expected to be slightly more intense up there although it looks like it's already started to ease."

Most places in the North Island are in for highs in the mid-teens today, with the coldest areas overnight still well above zero.

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That changes tomorrow when the remains of the cold fronts lashing the south today cross the Cook Straight, bringing showers with them.

The mercury drops a couple of degrees in the North Island, while below Nelson and Marlborough in the south it doesn't get above 8C.

The coldest parts of the North Island will be in Wairarapa and Hawke's Bay tomorrow night. Masterton could be in for an overnight low of -1C.