Summer is just around the corner but today it won't feel like that with bitterly cold southerlies accompanied by rain, hail and even snow in places.

MetService meteorologist Andrew James said New Zealand was under a "complicated trough", meaning there would be a lot of cold showers and even snow in parts of the South Island.

"Apart from a couple of fine spells in the upper North Island this afternoon, it is looking like a very cold, showery, unpleasant day for most people."

The wild weather period kicked off yesterday afternoon with a massive tornado that twisted through parts of Ashburton.

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James said there had been no more reports of tornadoes overnight, and any more were unlikely today.

Cold southerlies were expected to bring wintry conditions to the south of the South Island through today and into Tuesday.

The complex system would drop temperatures substantially about the country, with heavy rain, and even snow dropping to 400 metres in eastern parts of the South Island, with 30-40cm of snow expected above 800m.

A heavy snow warning was in force for inland Southland, Central Otago and inland Clutha.

Snow had been falling since last night in parts of the South Island, with the Crown Range Rd in Queenstown already with decent cover.

Road snow warnings are in place for Lewis Pass (State Highway 7), Arthur's Pass (SH73), Porters Pass (SH73), Lindis Pass (SH8), Crown Range Rd and Milford Road (SH94).

The North Island high country could see snow to 1000m.

People were advised higher roads could be affected by unseasonable snow, and wintry conditions could be hazardous for young stock. Horticulture and viticulture industries were also advised to stay up to date with the forecast as hail could be a risk in some areas.

There was a low risk of thunderstorms about the south and east of the South Island, with a moderate risk along the coast of southern Fiordland, Southland, Otago and Canterbury south of about Banks Peninsula.

There was also a low risk of thunderstorms about Buller and the ranges of western Nelson, and Northland as a front passed over this morning.

The wild weather would persist until Thursday, when a narrow ridge was forecast to move east across the country, being replaced by a moist northeast flow on Friday as a low developed in the Tasman Sea.

Today's weather

Whangārei

A few showers developing morning, clearing afternoon to fine breaks. 18C high, 8C overnight.

Auckland

​ A few showers, clearing afternoon. A fresh southwesterly change in the morning. 17C high, 10C overnight.

Hamilton

A few showers, clearing afternoon to fine spells. Southwesterly dying out. 17C high, 5C overnight.

Tauranga

A few showers, clearing in the evening. Southwesterly developing. 18C high, 7C overnight.

New Plymouth Showers, easing in the evening and clearing overnight. Southwesterly dying out. 15C high, 6C overnight.

Napier Occasional light rain in the morning, becoming frequent and heavier from afternoon. Cold southerlies developing. 19C high, 7C overnight.

Whanganui​ Cloudy periods, with showers clearing afternoon and fine spells increasing. Westerly dying out. 16C high, 5C overnight.

Wellington Mostly cloudy with a few showers. Southerly breezes. 14C high, 7C overnight.

Nelson Fine spells, a few showers. chance heavy with hail in the afternoon. Winds mainly light. 15C high, 5C overnight.

Christchurch Partly cloudy. Showers developing around midday, chance heavy with hail, easing evening. Fresh cold southwesterlies. 12C high, 5C overnight.

Dunedin Periods of rain with fresh cold southeasterlies. Snow possible about hill suburbs. Chance morning thunderstorms with hail. 11C high, 7C overnight.