The rescue co-ordination centre is reminding people to be prepared, as the MetService issues it's first heavy snow fall warning of the year.

Up to 50cm of snow is expected on the Lewis Pass and Porter Pass, with heavy rain in the coastal Canterbury.

Rescue co-ordination Centre NZ's manager, Mike Hill says you need to have a plan, and emergency supplies.

He says in terms of the weather if they can't get helicopters or ground teams in then people may be stuck until the weather clears.

A low pressure system from Tasman sea will join up with the front approaching from the Southern Ocean bringing cold air from near Antarctica.

Meteorologist Claire Flynn says it's the first heavy snowfall warning of the year.

Canterbury high country farmers are also hoping Monday's predicted snowfall wont last long.

Federated farmers mid Canterbury's president Michael Salvesen says it's been well flagged so farmers should be prepared.

He says there's very little young stock and as long as people keep them well fed they will keep warm.