Short, sharp storm leaves its mark
Blink and you might have missed it, the storm that was gone by lunchtime – and by breakfast in some parts of the country.
It came out of the west, caused a bit of chaos as it sped up the country overnight on Tuesday, then disappeared off to the east.
Powerlines and trees were blown down, blocking roads and cutting power in parts of the West Coast and upper South Island. Surging waves and rain also caused some flooding in houses in Nelson, while snow fell around Queenstown and Te Anau, parts of Southland and the Mackenzie Basin.
A damaged boat was rescued by Coastguard just before it washed up. It was left resting against a fence outside a house in the Nelson Harbour.
In the North Island, severe winds and rain buffeted, causing widespread power outages, flinging a trampoline into power lines and whipping Wellington with 154 kilometres an hour gusts.
The stormy weather was brought by an intense low, with an associated front, that had deepened quickly as it raced across the Tasman Sea. ‘‘It’s unusual in that it developed so rapidly but it’s not unheard of. We do get these from time to time,’’ MetService communications meteorologist Lisa Murray said.
The storm started with a low that developed on a trough off the northeast of Australia, moving into the Tasman Sea and deepening quickly. ‘‘We had very good development. All the ingredients for a low to develop very quickly.’’
The jet stream – ’’really fast air at a higher level’’ – which comes across the northeast of Australia at this time of year, helped with that development.
That low then combined with a small low that had been further south and picked up energy.
As the low moved across the Tasman, it started sucking cold air around it. That came from cold air coming up out of the south, not quite off the ice, but from the Southern Ocean near the ice south of Australia, Murray said.
There were also some active fronts associated with the low, with strong northwesterlies ahead of it reaching severe gale strength. Then behind it the low dragged up the cold air from the southwest.
The colder air at higher levels and warmer air below made things unstable, so there was a decent amount of rain.
The fact the cold air passed over at midnight and into early morning – the coldest time of day – contributed to the snow fall. There was also heavy rain at the time, which could lower the freezing level and enhance snow.
‘‘It’s not massive but it is a good dump,’’ Murray said. There were reports of 20 centimetres falling above 900 metres in Fiordland and 10cm above 400m in northern Southland, along with 5cm from Naseby and 3.5cm from Ranfurly in Central Otago.
While the stormy weather caused damage and moved quickly it did not reach the definition of a bomb low, which is how MetService described a bout of damaging weather that swept through the country in January.
Snow did fall during November in New Zealand, particularly in the South Island. Spring weather was changeable and could quickly go from warm to cold.
This year the cold change might have been particularly noticeable because it came after a warm spell, Murray said.
That thought was echoed by Queenstown-based NZ Ski marketing and communications manager Mel Tweedie: ‘‘We had that unseasonal heatwave last week – we were mid-20s all last week – then it rained at the weekend, now we’ve got this,’’ she said.
NZ Ski’s Coronet Peak was reporting 25cm of snow overnight. A snow event like that in November might happen every couple of years, Tweedie said.
By late morning yesterday the snow was beginning to melt around the base building, but up on the mountain it was nice and firm. About a dozen people were hiking to the top with their snowboards to ride down. Snowboarding in November was not common: ‘‘It’s usually mountain biking.’’