Christchurch and much of the South Island are bracing for the first significant blast of winter, with the NZ Transport Agency urging motorists to take extreme care on alpine roads and to avoid travel if conditions become hazardous.

Heavy snow is forecast to fall above 300 metres in Canterbury from Wednesday through to Thursday, with possible disruption to travel, trees and powerlines. Snow could fall to even lower elevations, according to MetService.

Drivers heading across alpine passes including SH73 from Porters Pass to Otira (Arthurs Pass), SH7 Lewis Pass, and SH8 from Burkes Pass to Twizel are being warned to plan ahead and monitor weather and road updates closely.

NZTA South Island System Manager Mark Pinner said cold conditions bring more than just snow-related risks.

“It’s not just snow on the ground that is a potential hazard, it’s heavy frosts and ice where the danger may not be as visible,” he said.

“People need to remember to adjust their speed to suit the conditions, to increase their following distances and use their headlights to be seen.”

Pinner said drivers should postpone trips during periods of elevated risk, if possible.

“If you can avoid or delay travel on roads while there is elevated risk, that’s sensible,” he said. “Stay up to date on the latest reports about the state highway network by visiting our Journey Planner.”

He added that NZTA is working with MetService to respond as the situation develops and said people should travel with warm clothing, food and water in case of delays.

Heavy rain is also forecast for Fiordland, and the Buller, Grey and Westland Districts between Karamea and Harihari, with drivers urged to take extra care and plan accordingly.