Weather: Antarctic air mass may spell coldest weekend of year so far

March is about to feel more like May, a forecaster says, as a surge of polar air brings what could well prove the country’s coldest weekend of 2024 so far.

Niwa forecaster Ben Noll said separate cooler air masses were due to move up the South Island today and tomorrow, before a larger flow began travelling northward around the end of the week.

“That’s the one I think most people are going to feel, as it’s going to progress up the whole country - and some temperatures will seem closer to late autumn,” Noll said.

“So, it might feel like a little jolt to the system and send some folks turning on the heater, particularly in the South Island.”

There was even a chance of a dusting of snow at elevation for inland parts of the south on Friday night.

“And because we’re expecting a southerly behind this front, it’s likely to be quite blustery on Saturday, so there’ll be a wind chill factor to go along with the cold snap.”

That day, temperatures in southern centres - including Invercargill, Dunedin, Queenstown and Christchurch - were forecast to reach only the mid-teens.

“Even in a place like Auckland, you might be struggling to get to 20C on Saturday,” Noll said.

“There’ll also be some chilly overnight temperatures in the period from the weekend and into early next week.”

For Saturday and Sunday, MetService was forecasting minimums of 12C for Auckland, 10C for Wellington and Tauranga - and just 7C for Hamilton.

Looking at the wider picture, Noll said a globe-circling pulse of rain and thunderstorms, called the Madden-Julian Oscillation, was moving quickly through the equatorial West Pacific.

“As it quickly passes across the Pacific, it’s going to generate an atmospheric response that is El Nino-like, while creating a pressure pattern around New Zealand conducive to air masses coming up from the south.”

While temperatures were expected to be generally above average in the North Island and in the east of the South Island over autumn, Noll said the coming cool spell could potentially make March a standout.

“There’s only been one month since 2017 where we’ve had a below-average monthly temperature - but March 2024 could potentially be in that discussion.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.