The country is shivering under a blanket of frost as we wake to the coldest morning of the year.

After a wild weekend of snow, sleet and gales a spectacular clear and still night has led to bone-chilling sub-zero temperatures across New Zealand.

At 5am Alexandra was -4C and Queenstown -1C while Taupo was -2C. Even some parts of Auckland struggled to make it above freezing with Whenuapai recording zero.

One of the night's chilliest temperatures was recorded at Pukaki Airport in the Mackenzie Basin where it dropped to -5.6C. But the Desert Rd, fresh from a weekend whiteout, was even cooler on a polar -6.2C.

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This morning some trains in the capital on the Hutt Valley line were disrupted by the freezing temperatures.

Further south Central Otago authorities warned motorists that frosts had left roads across the district in a treacherous condition. Grit had been laid over the slippery icy surface to improve traction.

The MetService says the wintry weekend that brought a taste of Antarctica to New Zealand, closing roads and plunging temperatures below zero, will give way to more settled weather this week.

The polar blast that moved up the country proved the culmination of a complex system that pulled cold air up from Antarctica and dropped it across the country, pushing the mercury down to -6.5C at Waiouru and -5.7C at Mt Cook overnight on Saturday.

MetService forecaster Tom Adams said the sequence began with a low pressure system that rolled in from the Tasman Sea last Wednesday, before it unwound into an open trough that swept over New Zealand late last week.

When the trough, together with a tongue of warm air, blew through, it left in its wake a southerly flow of cold air.

"And it was basically coming straight up from Antarctica," he said.

"So we've been left in this southerly flow, and embedded in that have been various cold fronts, the most significant of which was the one that crossed the South Island on Friday afternoon and evening, and then the North Island on Saturday morning and afternoon - this is what dropped the snow."

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Although snow depths were deeper at higher altitudes, 12cm was recorded in Kingston near Queenstown, and in Clinton, west of Balclutha, where 3cm was recorded.

The dumping forced the closure of SH87 and SH1 north of Dunedin, and when the snow-bearing front reached the North Island later in the day, there was enough to close the Desert Rd and leave a dusting on the hills from Wellington to the Bay of Plenty.

Snow closed the Desert Road. Photo / Supplied via Kirsty Harwood
Snow closed the Desert Road. Photo / Supplied via Kirsty Harwood

On the Desert Rd, a snow plough and other contractors were brought in to clear the road and allow trapped trucks and cars to get through.

Some made their way out without help but others had to be towed.

Saturday's heavy snow also caused major disruptions elsewhere, delaying flights, coating farmland and making driving treacherous.

Coronet Peak Ski Area Manager Nigel Kerr with his trusty snow dog, Oscar, in about 20cm of snow at the base building of Coronet Peak on Saturday. Photo / Frederique Gulcher
Coronet Peak Ski Area Manager Nigel Kerr with his trusty snow dog, Oscar, in about 20cm of snow at the base building of Coronet Peak on Saturday. Photo / Frederique Gulcher

But the wild weather was a promising sight for skiers with snow falling on Mt Ruapehu for the first time this year as well as further south at Coronet Peak and on the Remarkables.

If all goes to plan, Whakapapa ski field will open on June 10 and Turoa on July 1.

In the South Island, Mt Hutt ski area is scheduled to open on June 9, the Remarkables the following day and Coronet Peak on June 17.

The snow fell from a cold front, which was followed by strong southwesterly winds that whipped up sizeable swells around the country's coasts.

Wellington's south coast was battered by waves of up to 11 metres - cancelling Sunday afternoon sailings of the Interislander ferry - but even these were dwarfed by a monster 19.4m, near-record wave recorded in the subantarctic islands south of New Zealand.

Adams said Saturday would have been the coldest night of 2017 so far for many centres, including Raetihi and Arthur's Pass, which both recorded lows of -4.9C, Blenheim (-3.4C) Taupo (-2.3C), Methven (-2.2C), Hamilton (-2C), Timaru (-1.4C) and Hokitika and Whakatane (both -1C).

At Ardmore airport in Auckland, the temperature fell to 4.1C.

Adams said it wasn't unusual for such a big burst of Antarctic air to move across the Southern Ocean: "It's just that it happened to make its way to New Zealand.

"But you wouldn't expect a polar outbreak like this every day when you're at the end of autumn and start of winter."

Adams said a ridge moving across the country would soon take some of the chill out of the air.

A satellite image showing freshly-dusted mountains across the country, as at Sunday afternoon. Photo / MetService
A satellite image showing freshly-dusted mountains across the country, as at Sunday afternoon. Photo / MetService

Temperatures were forecast to pick up on Tuesday as winds swung around to the northwest and a spell of patchy rain returned to western parts.

Showers were expected to spread to other parts during the week, but the risk of further severe weather this week was low.

"It's not going to be a particularly dry or wet week, more of an average one, with bits of patchy rain and occasional bursts of wind."

Looking ahead:

Whangarei:

Monday:

High 15C, low 6C. Mainly fine, possible morning frosts.

Tuesday:

High 17C, low 9C. Partly cloudy. Light winds.

Wednesday:

High 19C, low 9C. Partly cloudy, chance shower. Northwesterlies.

Auckland:

Monday:

High 14C, low 5C. A crisp, clear day with early frost in sheltered places and light winds.

Tuesday:

High 16C, low 10C. Fine at first, cloud increasing from afternoon. Light winds.

Wednesday:

High 17C, low 9C. Partly cloudy, chance shower. Northwesterlies.

Hamilton:

Monday:

High 13C, low -1C. Crisp, clear day with morning frosts.

Tuesday:

High 14C, low 7C. Fine with early frost, then becoming cloudy. Light winds.

Wednesday:

High 16C, low 6C. Mostly cloudy, a few showers. Northwesterlies.

Tauranga:

Monday:

High 14C, low 5C. Fine with light winds.

Tuesday:

High 15C, low 9C. Partly cloudy. Light winds.

Wednesday:

High 18C, low 9C. Partly cloudy, chance shower. Northwesterlies.

Wellington:

Monday:

High 13C, low 10C. Fine at first with frosts in sheltered places. Cloud increasing afternoon. Northerlies strengthening.

Tuesday:

High 15C, low 11C. Mostly cloudy, chance evening shower. Strong northerlies easing.

Wednesday:

High 15C, low 9C. Mostly cloudy, a few showers. A southerly change.

Christchurch:

Monday:

High 12C, low 1C. Fine, with morning frosts. Northeasterlies developing in the morning.

Tuesday:

High 16C, low 4C. Fine at first with frosts, then cloud increasing with one or two showers developing. Northerlies dying out.

Wednesday:

High 13C, low 5C. Cloudy periods, chance shower. Southerlies dying out.

Dunedin:

Monday:

High 11C, low 5C. Fine, with morning frosts. High cloud increasing in the evening. Northerlies developing in the afternoon.

Tuesday:

High 14C, low 8C. Cloudy periods, one or two showers developing in the morning. Northerlies gradually turning southwest.

Wednesday:

High 13C, low 7C. Mainly fine. Northerlies developing.