Snow warnings ran in an almost unbroken line from the middle of the North Island to the top of the Southern Alps on Sunday, and forecasters say the coldest part of the outbreak is still ahead of us.
MetService had road snowfall warnings in place for five of the country’s most exposed stretches of state highway. The Desert Road (State Highway 1) and the Napier to Taupo road (State Highway 5) were both under warnings running into the early hours of Monday morning, with snow expected to settle on the road surface itself rather than just on the tussock beside it. In the South Island, warnings covered Arthur’s Pass and Porters Pass on State Highway 73 and Lewis Pass on State Highway 7. Lindis Pass on State Highway 8 and the Crown Range Road above Wanaka had picked up their share on Saturday.
The amounts were not enormous by alpine standards but they were enough to matter to anyone driving. Porters Pass was forecast to collect 10 to 15 centimetres about the summit, the heaviest fall anywhere in the country. Arthur’s Pass and Lewis Pass were each in line for 2 to 5 centimetres, with the Lewis Pass snow coming down to 400 metres. The Desert Road was expected to gather 3 to 6 centimetres about its summit from Sunday morning, and the Napier to Taupo road 1 to 2 centimetres from Sunday evening. Those figures come from the warnings MetService issued through the weekend.
By Sunday, MetService was forecasting overnight lows of about minus nine in some inland spots, with the Twizel and Mount Cook area close to double figures below zero. Snow was expected down to 400 metres in the Kaikoura ranges and to 600 metres in the North Island. Waiouru was picked as the coldest place in the North Island at about minus two. Heavy showers were forecast for Taranaki and Taumarunui in the morning.
MetService meteorologist Gerard Bellam said two separate systems were behind the cold, with wind watches around Cook Strait and Taranaki and a rain watch for the Wairoa district as a low northeast of the North Island pushed an east to southeast flow onto the country.
“We’ve got a good cold, wintry outbreak,” Bellam said. “These temperatures are still going to be below average for this time of year.”
The pattern that brings the snow is the same one that clears the sky afterwards, and that is where the sting is. Saturday night was not especially cold by winter standards, with Christchurch dropping to about 2C and Dunedin to 3C. Bellam said the sharp cold arrives once the cloud thins out and the ground radiates its heat away overnight.
“I’m seeing Monday morning in Christchurch a minus one, and colder down further south,” he said, pointing to lows near minus six in some inland places.
Open forecast model data from Open-Meteo, run independently of MetService, tells the same story about where the frost bites hardest. It puts Monday night’s low near minus five for Tekapo and minus four for Twizel, with Alexandra and Queenstown hovering around freezing and Christchurch and Nelson close to 2C. Those are valley floor grid figures and models routinely underdo the frost hollows of the Mackenzie country, so the real readings in the coldest inland basins are likely to be lower again. The useful point in the numbers is not the exact digit but the shape. Monday morning inland is colder than Sunday morning was, and the second half of the outbreak is the part that catches people out.
That is because ice does more damage than snow does. Snow on a pass is visible, it slows people down and it usually comes with a warning and a queue of cars fitting chains. Black ice on a straight piece of road at seven in the morning does not announce itself. The New Zealand Transport Agency said icy conditions were expected in many places once the snow had passed through, and asked drivers to check conditions before setting out, particularly on inland and alpine routes.
“In winter driving conditions where traction is affected, motorists are urged to reduce their speeds, increase their following distances, avoid sudden braking or turning movements and to stay as visible as possible,” an NZTA spokesperson said.
The agency said its contractors would monitor state highways and be ready to clear snow, or to close and restrict travel where that became necessary. All South Island state highways were open on Sunday morning despite snow moving through overnight, though NZTA asked motorists to take care where it had settled.
The North Island has had the wetter end of the same weather. Bellam said 135 millimetres of rain had already fallen in the hill country south of Gisborne from a separate low tracking away to the east. That rain had a physical consequence on Saturday, when rocks came down onto State Highway 35 between Waiau Road and Anaura Road, north of Mangatuna. NZTA crews cleared the fall during the day and then closed the road overnight from 9pm as a precaution, reopening it at 6am on Sunday with abseiling crews going over the face above the highway to check for anything else that had worked loose.
“While the road will reopen at 6am, there will be some stop go traffic management during the day as abseilers work in the area,” an NZTA spokesperson said. Drivers in the region were warned that further short notice closures were possible if more material came away.
None of this is unusual for the middle of August. What makes it worth paying attention to is the timing. The country is far enough into the second half of winter that people have started to relax about it, spring bulbs are up in Auckland gardens and the school holidays are a memory. A cold outbreak arriving now finds gardeners who have already put tender seedlings out, growers with fruit trees coming into bud in Hawke’s Bay and Central Otago, and drivers who have not thought about chains since July. Late frosts do more damage to an orchard than early ones because the buds have less protection by then.
The current warnings and watches are published on the MetService warnings page, and live highway conditions, including chain requirements and closures, are on the NZTA journey planner. Both are worth a look before an early start on Monday.
How cold did it get where you are, and did the snow reach further down than you expected? Tell us in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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