From Nelson and Blenheim to I' />

A large high combined with yesterday's cold change means frosts are likely across much of the South Island tonight.

From Nelson and Blenheim to Invercargill and Dunedin conditions are likely to be frosty overnight - prompting WeatherWatch.co.nz to give orchardists a heads up.

The North Island is expected to be frost free, despite a cold night on the way, due to windy conditions covering the entire island.

In saying that, there is still a moderate risk of winds not being strong enough to stop frosts in places like Wairarapa, Horowhenua and Manawatu, said Radio Network weather analyst Philip Duncan.