A wintry change has "sort of" arrived in the country.

That's as much as can be said of winter finally making its presence felt in the south of the country, WeatherWatch head analyst Philip Duncan says.

It's sort of that kind of winter.

Up top the weather is coming from across the ditch - more on what that means later - but for now a sou-westerly dragging freezing Antarctic air has arrived in the South Island.

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For the deep south, it means snow showers for some, including Queenstown, Alexandra, Gore and the hill suburbs of Dunedin, and chilly overnight lows for everyone.

The coldest populated area is expected to be the central Otago town of Alexandra, where temperatures will plummet to -3C overnight, Duncan said.

It will be -1C in Christchurch and 1C in Gore, Invercargill, Twizel and Timaru. Dunedin is expecting 3C.

But wind chill will make it feel cold even once the sun is up, with temperatures feeling like -10C in Queenstown tomorrow morning, and -5C in coastal parts of Southland, he said.

It's a different story further north - Wellington will drop to 6C overnight and Hamilton 7C, while Auckland will be comparatively tropical at 10C.

A front moving over Bay of Plenty, Waikato and Auckland this evening is already delivering rain and some thunderstorms.

The culprit was air blowing over from Australia and, not content with keeping temperatures high in the North Island, the westerly airflow would also impact on the polar blast, Duncan said.

"Into tomorrow that westerly will bulldoze the southerly out to the east. So we'll get a bit of warmth back to the South Island."

A second Antarctic change will arrive on Monday night, pushing north and giving the whole country a cold Tuesday.

But just a day later sub-tropical air will come down from New Caledonia, bringing warmth back to the north, he said.

"This is the weirdest winder I've ever seen. Over the last decade I haven't seen a winter that's had so many high pressure systems to our north-east, and that pulls warm sub-tropical air down."