3 Dec 2014

Otago's big freeze could break records

10:02 pm on 3 December 2014

New Zealand's coldest temperature could become a record weather extreme if a scientist's evidence is accepted by an international weather organisation.

The World Meteorological Organisation (WMO) is deciding if the minus 25.6degC recorded at Ranfurly, Central Otago, on 17 July, 1903 is the coldest recorded temperature for the Oceania region.

NIWA climate scientist Gregor Macara submitted a report to the world body which is expected to make a decision early next year.

Snow in St Bathans, Central Otago, photographed in July 1903 by F M Pyle.

Snow in St Bathans, Central Otago, photographed in July 1903 by F M Pyle. Photo: NATIONAL LIBRARY / Ref 1 / 2027137F

Mr Macara conducted a lengthy investigation on the temperature recording, which included hunting through newspaper archives, to try to find out what the weather conditions were in the lead up to the recording.

"Given that the observation occurred more than 100 years ago the information sources were quite limited so I was quite heavily reliant on newspapers of the time to gather together as much information on that weather event itself."

Searching through Otago Daily Times, Southland Times, Tuapeka Times and Mt Ida Chronicle archives he discovered there was a massive snow storm throughout the South Island on 10 July 1903.

In the days immediately following, the skies cleared under a high pressure system and enabled the temperatures to drop drastically.

A report in the Otago Daily Times on 18 July said the 2.10pm train from Dunedin to Ida Valley could not get beyond Middlemarch, as on arrival at the latter station it was found that no water could be got for the engine, the water in the tanks having been frozen into one solid mass.

Three days later, on 21 July, the paper reported: "Beef and mutton are frozen, and can only be cut with a saw or chopper, a knife being of no use. Turnips, potatoes and milk are also frozen, and the ink in the post office is in a similar state."

The minus 25.6degC temperature was recorded at Eweburn Nursery, where a plantation of pine trees had been established.

Mr Macara said there was a lack of information on the accuracy of the instruments used and the observation procedures were employed.

"We can't be 100 percent certain of the instruments' accuracy given there's no indication they were verified at the time, but on the balance of evidence there's no real reason to doubt it did get so cold."

The WMO keeps an official, unbiased list of world weather extremes and has a set of procedures to verify and certify records.

Mr Macara is now working on second report for the WMO on New Zealand's highest temperature of 42.4degC, recorded at Rangiora on 7 February 1973.

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