Every part of New Zealand is forecast to be colder than average tonight, and much of the South Island and central North Island will reach below, or near, freezing temperatures.

Christchurch, Queenstown, Hamilton, Timaru, Wanaka, Blenheim, Taupo, Alexandra, Ashburton and Waiouru are all forecast to reach 0C overnight.

Auckland will get down to 5C, Tauranga 4, Wellington 7, Nelson 1, Dunedin 6 and Invercargill 6.

Weather Watch NZ reported satellite animation of a "river" of polar air moving east over the country: "Low pressure just south of the lower North Island is tracking east and is pulling that southerly up behind it, so it will move into Wellington on Saturday afternoon then the rest of the eastern North Island overnight tonight/early Sunday."

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Shortly after 8pm Weather Watch NZ tweeted "heavy showers with hail now returning to Auckland after a quieter few hours".

"The southerly change looks likely to arrive at 6am Sunday when winds turn southerly and the skies dry up for a time."

The cause of the chill is a low pressure system off the east coast of the South Island producing cold southerlies and heavy rain along the South Island.

Up to 50cm of snow has fallen on New Zealand snow fields as the ski season opened at Mt Ruapehu in the North Island and Cardrona and Mt Hutt in the South Island.

At Mt Ruapehu, 150 skiers took to the slopes for its opening day today.

"Today has been exceptional for our Queen's Birthday opening. We don't normally get natural snowfall and are completely dependent on the snow factory," Mt Ruapehu's Whakapapa ski area GM Jono Dean said.

"We have been very lucky that Mother Nature delivered snow overnight to enhance the beginner ski and ride experience for the first day of winter."

But snow storms also played havoc with long-weekend travellers across the country's highways today.

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MetService issued road snowfall warnings for Desert Rd (SH1) east of Mt Ruapehu and the South Island's Lewis Pass (SH7), Arthurs Pass (SH73), Porters Pass (SH73).

MetService meteorologist Raveen Das said Desert Rd was the only one of four highways across the country where road snowfall warnings were unlikely to clear overnight.

"The overall trend for this evening is for snow showers to ease, the clearance really happens overnight, so there might be a few snow flurries affecting those roads," Das said.

However, tomorrow some clear sky relief is in store for long-weekend holiday-goers who spent today huddled in their rain-, hail- and snow-battered baches.

Most of the North Island will awake to showers Sunda but by the afternoon the deep low that caused today's stormy weather will have moved east of the country.

Highways across elevated stretches of New Zealand were closed today as snow fell in Canterbury and the North Island's Desert Rd south of Taupo.

Areas near Christchurch were also flooded.

Sunday however, Auckland and Tauranga will see highs of 14C, with showers clearing by late morning.

Wellington won't be quite so fortunate with a high of 9C and occasional showers, but the gale winds will ease throughout the day.

Hamilton will be 13C and fine. Whangarei will have a high of 15C with morning showers clearing.

MetService meteorologist Tamara Vuksa said the fine weather gradually emerging for the North Island Sunday will continue into Monday.

"We are on an easing trend. Auckland can expect fine spells in the afternoon Sunday with a few showers possible in the late evening," Vuksa said.

"The North Island will be mostly fine with a frosty start over central regions.

"On Monday there will be a ridge, very short-lived, that will bring mostly settled weather to everywhere except the lower South Island, Fiordland, Southland where showers will turn to rain with that next cold front coming on."

High winds affecting the lower North Island are setting in tonight and will last into Sunday, producing big waves in Cook Strait.

Niwa has warned rough surf may affect ferry operations in Cook Strait, highlighting: "The waves will grow even larger off Hawke's Bay with the biggest waves staying offshore."

Much of the South Island is set to reach freezing temperatures overnight, but will awake to clear skies tomorrow.

Christchurch has a forecast high of 9C tomorrow, Queenstown 8C, and Nelson 12C, but all cities will see near 0C overnight.

Dunedin will have a high of 10C tomorrow, becoming fine in the morning.

Invercargill will have a high of 10C with a few showers forecast.

"For the South Island most will see a fine start, there will be increasing cloud amounts but nothing special, it should be dry," Vuksa said.

Snow is forecast to return to mountainous regions of New Zealand on Wednesday or Thursday this week.