A "shot of cold air" is set to make landfall in New Zealand this weekend, with WeatherWatch warning it could impact roads, bring snow to sea level and put newborn lambs at risk of death.
The low pressure system will move up the country from the Southern Ocean on Sunday and Monday, with NIWA forecasting it'll result in icy winds and widespread snow.
The South Island is anticipated to cop the worst of the wintry blast.
"Windchill is pretty low with some exposed parts of Southland, Otago and Canterbury hovering around freezing for about 24 to 36 hours and dipping down to about -3 or -4 at times, like on Banks Peninsula," WeatherWatch says.
"However, wind chill from the polar blast a month or so ago was actually lower. The issue this time around may be that there is more wet weather, which can be the killer for newborn lambs when you add on the windchill.
"As for snow, heavy falls in the mountains and ranges of the South Island are fairly widespread too. Snow will be heaviest above 400m but snow flurries are possible down to low levels (100m) and there may be a snow/rain mix to sea level."
WeatherWatch says the peak cold will be before dawn on Monday, and predicts highways in both the South and North Islands will be impacted.
The North Island's higher-elevation areas are expected to get a dusting of snow.
WeatherWatch head forecaster Philip Duncan says a wind direction change, from southerly to south-westerly, will lift temperatures again on Monday night and through Tuesday.
A high will also inch towards New Zealand from the Tasman on Tuesday, bringing milder winds.
