Ice halo around moon in New Zealand
© Met ServiceThe ice halo was captured by the MetService's camera at Mt Cook.
A rare "ice halo" visible around the moon overnight coincided with a big chill, with temperatures dropping below freezing point in both the North and South Islands.

Ashburton was the coldest spot on Sunday morning, with an icy temperature of -3.4C between 5am and 6am. Christchurch dropped to -2.9C, while in the North Island, both Masterton and Hamilton were -2.7C. "They'll be waking up to a really cold start," MetService meteorologist April Clark said. Hamilton was probably having the worst start to the day, she said.

"They have a little bit of fog around as well - they cool and get frost, and they also get fog, which is a bit miserable." Temperatures dropped even lower on Saturday night in Queenstown, dipping to -3.6C between 9 and 10pm when the skies were clear, before "heating up a little bit" when cloud set in. "It's really a huge difference when you get cloud - it's just like a little blanket over everyone."

At the same time, an "ice halo" around the moon was visible from Mt Cook, where MetService's camera also captured snow on the Southern Alps overnight. "It looks pretty awesome," Clark said. "It's just scattered light around from the moon, the same way that you get it from the sun, and it looks quite pretty ... This is not something we see very often, actually."

MetService's website says ice halos are visible during days with "wispy high clouds in the sky made of ice". They occurred "when sunlight is refracted and reflected through ice crystals in clouds high up in the atmosphere. Some of these show rainbow colours, as ice crystals can act like prisms, separating the different colours of light."

Throughout Sunday, most of the country will be "pretty cold", but Hamilton and other western regions were expected to be spared the big freeze on Monday morning, thanks to cloud, while Canterbury and northern Otago faced a frosty start to the week.

On Sunday, the North Island was expected to be mostly fine with cloudy periods, with showers on the East Coast clearing, and isolated showers between Taranaki and Manawatu, and from Auckland northwards.

There will also be isolated showers on the south coast of the South Island and Buller, with cloudy periods on the West Coast and a mainly fine day elsewhere. The weather should remain fine until mid-next week, when further rain is forecast.