After a frosty start most of the country should clear for a fine and sunny winter's day.

MetService lead forecaster Michael Martens said clear skies in many places overnight let the heat out, and dropped temperatures well into the negatives.

The coldest temperature overnight was -5C down at Pukaki in the central South Island.

St Arnaud in the Nelson Lakes region dropped to -4C while the coldest North Island temperature was -2C at Tongariro.

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"As the sun comes up it should be a mostly fine day across the country, with only a few showers remaining in western areas," Martens said.

The next front would arrive this afternoon in the South Island, bringing a period of rain to Southland, Otago and Fiordland, spreading into Westland and Canterbury by the evening.

"It will be quite a vigorous front, with strong winds and potentially squally thunderstorms.

"A burst of cold wind behind it will bring a southwest change, with snow lowering to 400m in the South Island."

Road snow warnings were already in place overnight and this morning in the South Island for Arthur's Pass (SH73), Porters Pass (SH73), Lindis Pass (SH8), Crown Range Rd and Milford Rd (SH94).

The front would arrive in the lower North Island tomorrow morning bringing showers with it, but it would weaken as it moved further north through the day.

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"Generally the weather will gradually clear on Thursday across the country, with only a few showers remaining in the upper North Island from Coromandel to Northland."

Friday was not looking too bad either thanks to a ridge of high pressure across the North Island and east of the South Island.

The West Coast of the South Island would start to feel the effects of another system out in the Tasman Sea on Friday.

"That system will rotate on Saturday closer to New Zealand, spreading rain to most places late Saturday and into Sunday," Martens said.

"So the weekend is not looking too nice, quite changeable with rain."

Today's weather

Whangārei

Cloudy periods. Westerlies. 16C high, 7C overnight.

Auckland

​ Cloudy periods and isolated showers. Westerlies. 15C high, 9C overnight.

Hamilton

Cloudy periods and morning frosts. One or two showers. Westerlies. 14C high, 4C overnight.

Tauranga

Sunny spells. Westerlies. 15C high, 5C overnight.

New Plymouth Cloudy periods. A few showers, mainly from afternoon. Westerlies. 14C high,7C overnight.

Napier Fine with morning frosts. Northwest breezes. 16C high, 6C overnight.

Wellington Fine. Northerlies picking up in the afternoon. 12C high, 7C overnight.

Nelson A frosty start to a fine day. Light winds. 13C high, 3C overnight.

Christchurch A fine day with gusty northerlies. Showers developing late evening with a strong southwest change. 14C high, 3C overnight.

Dunedin Fine with gusty northwesterlies. A period of sleety evening rain with a strong southwest change. 13C high, 4C overnight.