Cold snap looming as slow-moving low-pressure system moves over New Zealand

Auckland is looking at a sunny afternoon before rain sets in tomorrow. Photo / File

New Zealand, make the most of the good weather this afternoon if you've got it because a cold snap bringing rain, snow and southerlies is on the way.

Unstable conditions might bring showers to some this afternoon but most areas are looking to continue the weather of high cloud with northerlies.

Elsewhere, showers in the Northland area today are likely to sink down the country southwards today and into tomorrow.

Showers should be expected to hit the Auckland region by the afternoon but rain will be heavier in Whangaparaoa and Great Barrier Island.

Last week was well above monthly averages, with benign and cloudy weather keeping the frosts at bay.

The last time the temperature dropped below freezing at Christchurch airport was 10 days ago, with the last week average being 8.4C - the monthly average is 5.8C.

Meanwhile, Wellington was 1.2 degrees above average with 10.1C last week, and Auckland's normal July temperature being 10.9C, but so far has averaged 11.8C.

Will it snow next week?
A weak trough drifts over NZ next week, then on Tuesday an upper trough gives it support. Separate low centres intensify, the location of which affects how low + how much snow esp 4 Canterbury on Weds. Watch out for updates on https://t.co/ePtVj8cXwp ^TA. pic.twitter.com/ad9c6QqrOX

— MetService (@MetService) July 27, 2019

MetService meteorologist Tom Adams told the Herald a high-pressure system lying over the Chatham Islands is behind the abnormal winter weather.

The air is moving around the system anti-clockwise, he said, feeding the nation with warm, moist air from the northeast.

"That's bringing down warmer air, lots of moisture, cloud and plenty of warm weather - that's what's keeping us warm overnight," he said.

"If the high pressure was parked over New Zealand, we'd have clear skies, very little wind and very cold nights, which would help bring the temperatures down.

"Even though it would be warm in the middle of the day, it would get cold at night ... under those pressure conditions."

But next week brings back some winter reprieve for cold weather lovers and MetService advises snow might fall in parts of the country too.

"What starts as a fairly weak system suddenly gets amplified and localised low-pressure systems deepen within it," Adams said.

"If a good low forms east of the South Island that would be the perfect recipe for a dump of snow in Canterbury and Otago.

"At present, we are expecting snow in Canterbury to 600m, but that could easily be lower once the models show more agreement."

Monday's weather outlook

Whangarei: Showers, possibly heavy at night. Easterlies, turning northwest at night. High 17C, Overnight 9C.

Auckland: Partly cloudy, with a few showers north of Whangaparaoa, and the odd afternoon and evening shower elsewhere. Northeasterlies. 17C, 10C.

Tauranga: Mostly cloudy with a few showers. Light winds. 16C, 8C.

Hamilton: Cloudy periods. Easterly breezes. 17C, 7C.

Napier: Early fog possible, then mainly fine. Light winds. 15C, 5C.

New Plymouth: Fine. Rain developing overnight. Northeasterlies. 16C, 8C.

Wellington: Mainly fine, some evening cloud. Northerlies. 15C, 8C.

Nelson: Partly cloudy, chance morning shower. Rain at night. Northerly breezes. 14C, 7C.

Greymouth: Partly cloudy. Rain, possibly heavy, developing in the evening. Northeasterlies. 13C, 8C.

Christchurch: Fine with high cloud. Northeasterly dying out at night. 15C, 5C.

Queenstown: Fine with high cloud. Northeasterly dying out at night. 13C, 2C.

Dunedin: Cloudy. Light rain at times, especially from afternoon. Northerly breezes. 13C, 7C.

Invercargill: Occasional rain. Light winds. 11C, 2C.