The cold spring is expected to continue with rain, snow, thunder and chilling winds set to hit the country from tomorrow.
Conditions were expected to clear in the South Island on Thursday, but the cold weather would reach the North Island on early Thursday.
The weather was likely to persist in the North Island through Friday, he said.
MetService forecaster Oliver Druce said the cold flow would bring thunder, hail and rain to Canterbury and would hit Wellington in the early hours of Thursday.
"It's going to be a humdinger. It's too far out to forecast road snow for the North Island, but it looks like it will get down to 600 or 700m," he told NZPA.
Snow is expected on the higher roads in the South Island.
The MetService forecasted rain in Arthurs Pass to turn into 2cm to 4cm of snow possibly accumulating on the road on Wednesday evening.
Similar conditions were forecast for Porters Pass, but with heavier falls of 4cm to 8cm on the road.
On the Milford Road, rain was expected to turn to snow on Wednesday afternoon, with 3cm to 5cm accumulating.
