MetService has issued a Heavy Snow Warning tonight for Clutha and Southland, including Stewart Island and Fiordland south of George Sound.

The warning is starts tonight at 6pm and ends on Monday (August 5) at 1pm.

Snow is forecast to lower to sea level. Expect 15 to 20cm of snow to accumulate above 100 metres, with even deeper snow expected at higher levels and drifts.

Heavy snow may disrupt travel in affected areas and could damage trees and powerlines. Cold conditions may cause stress for livestock.

An update for severe weather will be issued by MetService by 9:00pm tonight (August 3).

An active front, followed by a very cold southwest change, is forecast to move north across the South Island tonight (Saturday) and Sunday morning bringing snow down to low levels.

The heaviest snow is expected above 100 metres in Southland, Clutha and southern Fiordland, and a Heavy Snow Warning is in force for these areas.

A Heavy Snow Watch is in places for many other parts of the South Island.

In addition, a brief period of heavy rain is expected in Westland and a Heavy Rain Watch is place, while westerly gales may become severe in exposed parts of southern Hawkes Bay and northern Wairarapa for a time Sunday morning and a Strong Wind Watch is in place.

Snow is expected to affect many roads and passes causing significant disruption to transport, essential services and may cause stress to livestock. People are advised to stay up to date with the latest forecasts.