School holiday nightmare: winter arrives with vengeance across South Island

Snow is set to blanket vast tracts of the South Island tomorrow as a miserable school holiday storm sweeps across the country.

With snow expected to low levels across many regions mainlanders are being told to prepare for days of travel disruption and get stock to safety before the weather turns.

Much of New Zealand can expect to be lashed by heavy rain, snow and gales over the coming week.

Even the hills around Wellington could see snow flurries mid-week.

MetService is warning the vicious cold front is expected to hit overnight and last for the next four days.

Snow is expected to fall to very low levels in the south of the country with potentially damaging gales, torrential rain and snow lashing the country from Gisborne south.

Weatherwatch.co.nz is forecasting the snow to fall down to sea level across Southland and Otago tomorrow night with virtually nowhere in the South Island escaping a wintry white-out.

Coastal regions are being put on alert with possible flooding from strong onshore winds, high waves and heavy rain colliding in the storm. Sailings across Cook Strait could be in jeopardy with Niwa predicting waves of up to 4m by Thursday.

Snow is expected to fall for two straight days across the South Island - in some areas down to 100m in southernmost regions and down to 200m in Canterbury - followed by a bitterly cold southerly wind.

A severe weather watch for significant snow fall below 500m has been issued for Southland and Fiordland from overnight until Wednesday afternoon and Otago from Tuesday morning until Wednesday evening.

Canterbury and Marlborough can expect snow from Tuesday evening through to Thursday morning.

A swathe of road snowfall warnings have come into effect for key alpine passes and Dunedin's northern highway for the coming days.

Some alpine areas are expecting to get up to 1m dumping of snow over the coming 72 hours.

Potential snow accumulation through 12am Thursday.

For the mid & upper South Island, this represents only about 1/2 of the storm! ❄️🌨☃ pic.twitter.com/1aeuwSlWcH

— NIWA Weather (@NiwaWeather) July 9, 2017

MetService forecasters say snow is likely to fall down to 200m at times with up to 30cm or more accumulating on Otago and Canterbury high country stations.

It's expected to affect many higher roads and cause problems for livestock from Southland to Banks Peninsula.

The weather is set worsen as it tracks north with severe gales, heavy rain and snow set to strike the centre of the country.

Gales are expected to batter Taranaki to Gisborne south and heavy rain is expected to fall across the lower half of the North Island.

Snow is expected to bring disruption to central and eastern areas with forecasters predicting it will fall down to 600m across Wairarapa, Hawke's Bay and east of Taupo.

Weatherwatch.co.nz says the Wellington region could be hit by snow flurries down to 500m by dawn Wednesday.

The weather is not expected to let up until Friday when it moves away from the North Island.