South Island motorists are being warned not to be fooled by Thursday’s relatively mild temperatures, with heavy snow, severe winds and possible road closures forecast over the coming days.

Warm northwesterly winds are expected to lift temperatures to about 16C in Christchurch on Thursday, but conditions are forecast to deteriorate sharply as a cold southerly flow moves up the island.

MetService has issued strong wind watches for parts of the South Island, with northwesterlies potentially approaching severe gale strength in exposed areas of the Canterbury high country.

Motorists are being urged to take extra care when travelling in gale-force winds, particularly those driving high-sided vehicles, towing trailers or caravans, or riding motorcycles.

Conditions are expected to become colder on Friday, with strong southerly winds potentially approaching severe gale strength in Coastal Otago, Coastal Southland, Southern Fiordland and Stewart Island.

Christchurch, Banks Peninsula and the Canterbury Plains about and east of Lincoln could also experience southwesterly winds approaching severe gale strength in exposed places on Friday night.

Forecasting provided to New Zealand Transport Agency (NZTA) indicates heavy snow could fall across Canterbury’s alpine passes on Friday.

Between 10 and 20 centimetres of snow is possible around and west of Arthur’s Pass, affecting State Highway 73, with further snow expected near Lewis Pass on State Highway 7.

Snow could fall to elevations as low as 200 metres on Saturday, although lighter falls are expected across the Mackenzie Basin.

State Highway 94 near Milford Sound is also expected to be affected by snow. The road is due to close at 5pm on Thursday between the Lower Hollyford Road turnoff and The Chasm.

The section is expected to reopen late on Friday morning, although further snow showers could cause additional disruption throughout the day.

NZTA warned other state highways could be closed if snowfall made conditions unsafe.

Road users were encouraged to check weather and highway conditions before travelling and carry warm clothing, food and water in case they encountered delays, closures or detours.

Motorists driving in snow or icy conditions should reduce their speed, increase following distances, avoid sudden braking or steering movements and ensure their vehicle remains as visible as possible.