A frigid southerly outbreak is set to send temperatures plunging across the country early this week.

Hamilton and Taupō are forecast to record overnight lows about 8C below average for this time of year, while frosts could reach as far north as Northland.

The change follows a bitter weekend that saw flights cancelled, highways closed and cars stuck in the snow.

MetService meteorologist Michael Pawley told the Herald the wintry blast would spread up the South Island today before reaching the North Island overnight.

“As the winds turn southerly, it’s dragging air all the way up from the Southern Ocean, straight out of the coldest part of the world,” he said.

While several North Island locations recorded their lowest temperatures of the year last week, Pawley said the incoming chill was notable even by midwinter standards.

Hamilton is forecast to fall to -4C on Tuesday and again on Wednesday, compared with an average minimum of 4.7C for this time of year.

Napier could reach -3C, with Dannevirke, Masterton and Levin falling to -4C and Whanganui to -2C.

Levin’s forecast low is almost 10C below its early-August average minimum of 5.6C.

“There’s a chance of frosts for even as far north as Northland on Tuesday through to Wednesday. So yeah, it’s looking to be pretty cold,” Pawley said.

“Bands of rain” are forecast to move up the South Island today, marking the arrival of the colder air.

Christchurch will be dry but potentially “a bit gloomy” beneath high cloud this morning before cold winds and showers develop.

Snow could lower to between 200m and 300m across parts of Southland and Otago by this evening.

The North Island will largely be fine, dry and sunny today, although Auckland can expect some cloud and the odd shower.

Wellington will begin with fine weather before cloud increases and a few showers arrive with the cold front this evening.

By tomorrow, the cold air will have spread across the country, with showers moving up the east coast and bringing what MetService called a “real wintry flavour”.

Christchurch can expect cold winds and showers, while snow is possible about higher ground in the lower North Island, including the tops of the Remutaka Range.

The southerly will also whip up waves of up to 6m along parts of the Wairarapa coast. A 12-hour Heavy Swell Warning is in force from noon tomorrow for the coast between Ngawi and Flat Point.

Despite the bitter starts, Wednesday is expected to deliver generally fine, sunny weather beneath a ridge of high pressure.

Another cold night is forecast into Thursday, although most places should remain dry during the day.

Wetter weather is then expected to approach from the west on Friday, similar to last week.

Pawley said the main impact of the outbreak would be the chill rather than significant snow or hazardous weather.

“It’s just mainly going to be bitterly cold.”