Winter conditions apply to the Crown Range Pass and the Lindis Pass.
Motorists should drive slowly and carry chains, Downer EDI supervisor Michael Scott said yesterday.
Road crews were able to open both alpine passes about mid-morning yesterday after they were closed by an overnight dump of snow.
Conditions remained "drizzly and ugly" yesterday and motorists could be confronted with dangerous frosts this morning, Mr Scott said.
"It's a bit like crystal-ball gazing, but if we get a frost, it will be diabolical," he said.
Public chain-fitting advice is available in Wanaka today at Wanaka Tyres and Autos, and at the Queenstown Event Centre tomorrow.
