Shotover River may freeze, says forecaster

Shotover Jet operations manager Simon Thew with one of the chunks of ice which clogged the river....
Shotover Jet operations manager Simon Thew with one of the chunks of ice which clogged the river. Photo by Chris Morris.
Sub-zero temperatures which could freeze the Shotover River have been predicted this winter by long-range weather forecaster Ken Ring.

However, other weather and climate forecasters are less sure there will be a deep freeze this winter.

Mr Ring said he took into account the moon's effect on tides, and also the air pressure and land.

"There is a tide in the air that is as measurable as the tide in the seas," Mr Ring said.

As well as the monthly cycle, he looked at its longer repetitive cycles, of between nine and 11 years.

"I'm looking at the last time it froze and the time before . . . People have short memories."

According to his calculations, winter in Otago would arrive suddenly, with temperatures below freezing from early May.

He said the weather would improve on the Otago coast by the end of August, but Queenstown and Wanaka would remain in the grip of a hard winter - possibly until November.

This winter would only be the start - Mr Ring said the winter of 2011 might rival the bitter winter of 1939, when snow blanketed the country.

Shotover Jet spokesman David Kennedy said the company was aware of the problems ice could cause - in July 2007 a week of frosts saw car-tyre sized ice blocks floating down the river and trips had to be cancelled until they cleared.

Queenstown Rafting operations manager Guido Leek said ice disrupted rafting trips, at some point, most winters, "The water doesn't completely freeze over . . . it is like a margarita mix."

Further back, sections of the Shotover near Skippers Canyon froze from bank to bank in July 1991 and again in June 1992.

However, MetService weather ambassador Bob McDavitt said the extreme cold of those years was triggered by the 1991 eruption of Mt Pinatubo, in the Philippines, which sent billions of tonnes of dust into the atmosphere.

"For it to get that cold again this winter, you would have to have a volcano erupt tomorrow," Mr McDavitt said.

He was unable to give a forecast for the winter at this point, because MetService takes readings from sea surface temperatures which could change month to month.

But he did say sea temperatures were "trending up", which should bring warmer weather during February.

National Institute of Water and Atmospheric Research (Niwa) climate research scientist Darren King said the institute usually only forecast three months in advance.

"There are very few places around the world that will give a forecast for six months out, and those that do come with some sort of warning," he said.

The latest Niwa report for February, March and April shows the temperatures for inland Otago should be "average".

While mainstream weather forecasting paid attention to lunar and solar cycles, he said there was "a lot of variability" and different factors which could affect weather patterns on Earth.

Queenstown-based weather forecaster David Crow was also sceptical of Mr Ring's prediction, as a hard winter would buck a trend towards warmer overall temperatures.

"Last year was a warmer year, on average, by 1.3degC," he said.

Last year, only one month, August, had been colder than average and winter had been milder than usual overall.


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