Severe frosts and black ice are on the way for parts of New Zealand this weekend as another surge of polar air is set to slam the country.
The cold air is forecast to come into the lower South Island later on Friday and overnight into Saturday morning, bringing gales, snow and "bitterly cold" temperatures, according to WeatherWatch.
From Sunday night overnight lows will "dramatically drop", with the mercury expected to fall to between -7C to -12C in the South Island's high country, while central Otago and northern Southland will see overnight lows down to -4C and -6C. Queenstown and Arrowtown will drop to -2C to -4C in some places.
"From the polar blast last week to the cold southerly this week lingering into next week we're certainly into peak winter right now," WeatherWatch head forecaster Philip Duncan.
"From late June to mid August, New Zealand often experiences the depths of the winter cold in the most consistent day-after-day manner".
Duncan says high pressure will move in later this weekend and into next week after the "surge of polar air" arrives on Friday. That high pressure will then "lock in this cold and create for severe frosts in the South Island's interior and heavy frosts for some in the North Island".
WeatherWatch warns the wet and snowy weather falling in parts of the country on Friday night and Saturday morning will "significantly increase the chances of black ice, mostly on South Island roads and highways".
"Black ice is caused when water (from rain or snow melt) freezes overnight and is impossible to see. Daytime heat may melt it, but it refreezes each night until the moisture has gone. Black ice is most likely found on tight, shady, corners but can also be found on stretches of straight open road. Motorists should take extra care and be extra vigilant to the 'skidding' road signs showing ice, some of which are up all year around but now is the time those road signs matter most."
In the North Island, the Central Plateau will see the coldest temperatures, with overnight lows around Waiouru, Ohakune and National Park getting down to -4C next week.
WeatherWatch says the cooler temperatures will continue to be felt until well into next week.
"Despite the low being north of New Zealand and with sub-tropical connections the cold air brought in right now by the Southern Ocean southerly will linger for much of next week, bringing a colder than average week to a number of regions."
According to MetService, a road snowfall warning is in place around Dunedin to Waitati Highway (SH1) from Friday afternoon to Saturday morning, while a strong wind watch is in place on coastal areas from Otara (Southland) to Dunedin, as well on Stewart island.
