If autumn has felt a lot chillier than usual so far, you’re not imagining it: last month was New Zealand’s coldest March in more than a decade.

And a fast-approaching winter is likely to be decidedly different to what we’ve experienced over the past five years, a meteorologist says, with more variability in the mix.

Niwa reports last month’s mean temperature finished up at 14.8C, which, at nearly 1C below the average, made for the coolest March in 12 years.

The month saw some wild temperature swings – compare the hottest temperature of 32.6C at Clyde on March 2, with its coldest, -4.9C at Waipara North on March 16 – and plenty of dryness in places.

While rainfall remained below or well below normal across most of the North Island, parts of Waikato, Fiordland, and Southland saw rainfall levels either above or near normal.

The biggest one-day deluge came with the 117mm recorded at Milford Sound on March 25, while a day later, the month’s highest wind speed came with a 178km/h gust registered at Cape Turnagain.

Niwa meteorologist Ben Noll says the month’s colder flavour is partly explained by the polar jet stream bringing its chilly influence closer to New Zealand over March, with more southerly and southwesterly flows reaching the country.

At the same time, he said, the subtropical jet stream was positioned well to the north.

“Basically, there were no air masses that came down from the tropics to affect New Zealand over the course of a whole month, which is pretty unusual.

“You’d have to go back to 2012 to have a March that was this cold.”

This climate set-up also deprived many regions – including drought-stricken Marlborough – of much-needed moisture.

Another major influence had been the tail of a since-faded El Nino climate system, whose handprints could be seen in widespread dryness across New Zealand’s north and east, but plenty of rain in the south and west.

By winter, however, Niwa anticipates the country will be in an “ENSO-neutral” regime – meaning that neither El Nino or La Nina would be dominant factors.

Ben says this will prove a big change from last year’s El Nino winter – but also the three La Nina winters before it, which went down as back-to-back record-warm seasons.

“I think the weather personality of this winter may be quite variable, when you step back and look at June versus August.”

Niwa’s outlook for April to June, at least, picks near average temperatures in the west of both islands – and either near or above average temperatures elsewhere.

Later in the year, meanwhile, there were increasing signs of La Nina returning: although it's too soon to say whether New Zealand was in for the same warmth and relentless wet of this decade’s first three years.

“We’ve seen cool spells over winter, but maybe winter won’t be as sharp in that regard.

“And if we see that expected trend toward La Nina as the season goes along, then maybe that’ll introduce more moisture into the picture over the second half of winter.”

-NZ Herald.