The coldest night of the year

Last night was the coldest of the year so far for most of the country. File photo.

Last night temperatures for many major centres hit the lowest seen so far this year.

Although no long-standing records were broken, the cold snap would have got heat pumps fired up from Auckland, which dropped to 1.4C at the airport - the coldest seen since July 2015 - to Mount Cook airport, where snow on the ground enabled the second night in a row below -13C.

The cause of the low temperatures was a ridge of high pressure over the country, meaning clear skies and light winds.  The coldest locations were ones still holding onto a covering of snow from the middle of last week, when extensive snow fell in inland Canterbury, but also a few flurries as far north as the Desert Road.

“A covering of snow reflects the sunlight away from the ground, but still allows heat to escape,” says meteorologist Tom Adams. “This means the ground cools further each day, chilling the air at night.”

A weather station near Tekapo measured -12.0C overnight Friday night, and -11.8C on Saturday night, and only crept up to -0.4C during the day between them.  Photos on Twitter have shown the shoreline of the lake freezing over.

The clear skies and icy temperatures have been good news for ski fields, but have made for slippery conditions on the roads.  Tonight will be also be on the cool side, but winds switching back around to the north should ensure it is a touch warmer than last night.

Cloud building along the west of the South Island heralds the arrival of a front bringing warmer air, and also marks the end of the cold snap. As the front progresses north most of the rain will be in the west, with heavy rain warnings out for Fiordland and southern Westland on Monday.

A low forms on the front over the Tasman Sea, which will affect the country late on Wednesday. Easterly winds as the low approaches the North Island will be one to watch, with a chance of heavy rain in the Far North, but also a chance of lighter rain for Otago and Canterbury which are still trying to dry out from the heavy rain over a week ago.

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