Farmers have been asked to monitor stock, as much of the Otago and Southland region comes under a heavy snowfall warning at an "unusually late" time of year.
MetService says front moving over the South Island and on to the lower North Island today would be followed by a cold southwesterly flow that could bring snow to sea level in parts of the South.
The forecaster yesterday issued snow warnings for many South Island highways, including the alpine passes and Dunedin’s Northern Motorway (State Highway 1).
Southland's Milford Road (SH94) is expected to get up to 15cm of snow and will close at 4.30pm today.
MetService head of weather communications Lisa Murray told RNZ's Morning Report programme several places in the country, including Dunedin, would have warm temperatures ahead of the cold front.
The city would reach a maximum of 21degC on Thursday, but on Friday that would drop to as low as 8degC, with an overnight temperature of just 3degC.
"Where possible, potentially move stock to more sheltered areas, to keep everyone warm and well fed. Soil temperatures have been increasing over the past week, so I would not expect any snow to hang around for too long."
The sudden cold blast could prove a challenge for those farmers who were still lambing, she said.
Southland, Clutha, Dunedin, Central Otago and Southern Lakes would also be under a heavy snowfall watch for 18 hours from 4pm today.
"Snow is expected to lower to near sea level. Heavy snowfall is possible above 300m, where amounts may approach warning criteria."
'Short and sharp' cold snap
MetService meteorologist Alex Holden said much of Otago would have heavy snowfall warnings about 300m above sea level, with Dunedin also in the firing line.
"It is fairly unusual to get snow this low and this intense at this late time of the year."
The worst of the cold snap, which could bring sub-zero temperatures to parts of Otago and "low single-digit" figures for Dunedin, would occur tomorrow morning, he said.
"A lot of people will wake up to snowy white caps on the mountains."
But the cold snap would be "short and sharp", he said, with conditions rebounding on Saturday and Sunday, although he expected Saturday to be a "bit cloudy and miserable".
"It is not unlikely we will get another cold front very shortly. Whether it will be as intense as this one is hard to say."
Road snowfall warnings
Waka Kotahi NZ Transport Agency said road snowfall warnings were in place from late today into tomorrow on the Lewis Pass (SH7 - Canterbury/West Coast), Arthur’s Pass (SH73), Haast Pass (SH6), the Lindis Pass (SH8, between Cromwell and Omarama), the Crown Range Rd between Queenstown and Wanaka, the Milford Rd (SH94) and the Dunedin to Waitati Highway (SH1).
Journey planner Nicole Felts urged extra caution on the road and to expect wintry conditions. She told RNZ's Morning Report people may not be expecting snow down near sea level in places like Otago and Southland at this time of year.
"[We're] asking that people drive a bit slower than they normally would and make sure that they're accelerating smoothly, braking gently, taking their time if they do absolutely need to travel tonight."
Meanwhile, strong winds are likely for Otago and Southland until about midday today, while heavy rain warnings are in place for Buller, Westland and the headwaters of Canterbury lakes and rivers about and south of Arthur's Pass.
Fell urged caution for road users driving in heavy rain or winds.
Highways affected
Dunedin to Waitati highway (SH1)
Period: From 10pm on Thursday until 6am on Friday
Snow may briefly affect the road for a time tonight and early on Friday morning, and 1cm to 3cm may settle on the road near the summit. Note, another burst of snow is possible later on Friday, and this warning may be extended.
Milford Road (SH94)
Period: From 3pm on Thursday until 6am on Friday
Rain forecast to turn to snow near the Tunnel this afternoon, then gradually lower to near sea level early on Friday morning. Expect 10cm to 15cm of snow to settle on the road above 800 metres, with lesser amounts down to near sea level.
Crown Range Road
Period: from 9pm on Thursday until 5am on Friday
Snow forecast to briefly affect the road for a time tonight and early on Friday morning, and 2cm to 4cm may settle on the road.
Lindis Pass (SH8)
Period: from 10pm on Thursday until 6am on Friday
Snow expected to briefly affect the road for a time tonight and early on Friday morning, and 1cm to 3cm may settle on the road.
Haast Pass (SH6)
Period: From 9pm on Thursday until 6am on Friday
Rain set to turn to snow tonight. Expect 2cm to 5cm to settle on the road near the summit, with lesser amounts down to 300 metres.
Arthurs Pass (SH73)
Period: From 12am to 8am on Friday
Rain expected to turn to snow tonight. Expect 4cm to 8cm of snow to settle on the road above 800 metres, with lesser amounts at lower levels.
Lewis Pass (SH7)
Period: From 1am until 2pm on Friday
Rain is forecast to turn to snow tonight. Expect 4cm to 8 cm of snow to settle on the road above 800 metres, with lesser amounts at lower levels.
- additional reporting by RNZ and ODT Online
