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With 1degC frosts predicted to hit the Queenstown area this morning and possibly colder temperatures tomorrow, a close watch is being kept for potential frost damage.
Veteran grape-grower and wine pioneer Alan Brady said the unusually low snow-line in the district meant a high risk for the region's vines, which were at a vulnerable stage.
In the 27 years since he first planted grapes in the Gibbston Valley, he had never seen the snow as low or as heavy as it had been this week.
Cromwell winemaker Rudi Bauer said frost-fighters turned on wind machines and sprinklers early yesterday to ward off the effects of a 1degC frost.
Mr Bauer said the next two days were crucial, and if temperatures dropped to -5degC, there would be little some owners could do to protect their vines.
"What we really need is an 18 degree day on Friday [today] and hopefully that will warm up the ground and prevent any serious frosts."
While some vineyards, such as Chard Farm, had helicopters on standby on Wednesday night, most were relying on wind machines and natural airflow to see them through this morning's cool conditions.
Chard Farm Vineyard viticulturist Michelle Crawford said the vineyard managed to get through the last two nights without using helicopters, but expected tomorrowmorning would be the "big one" .
"We'll certainly be watching."
So far, natural airflow had helped prevent damage at Chard Farm, where cool air drained into the Kawarau River valley, she said.
Further up the Gibbston Valley, Mt Rosa vineyard owner Jeremy Railton said the southerly winds kept temperatures just above freezing during the past few nights.
"As long as it stays southerly, it's OK."
Northwesterly weather predicted for tomorrow could bring calm conditions and colder temperatures with the snow around, he said.
Gibbston Valley Wines viticulturist Dominic Mondillo, who also manages the company's vines and his own vineyard at Bendigo, said in addition to the snow and frosty conditions, the prolonged spell of cold temperatures was holding back grape growth.
"Not a whole lot's happening in these conditions.
''We are waiting for late spring to arrive."
Mr Brady said the next two to three weeks were vital to get the vines through their most vulnerable stage and predicted every helicopter in the South Island would have been booked this week.
However, he said risk of frost damage was part of growing grapes in Gibbston.
"The best wines come from the more marginal regions."
The MetService is not predicting an improvement in the weather until at least tomorrow.
In the meantime, vineyard owners and staff - and helicopter owners - face some sleepless nights as they try to protect crops.