MetService this morning warned of periods of heavy snow above 500 metres for Central Otago which may disrupt travel and damage powerlines.
"Prepare for snow, cold temperatures, and possible power outages. If you must travel, drive cautiously, and ensure you have snow chains, sleeping bags, warm clothing, and emergency items."
The warning covers the period from 6pm on Thursday to 9am on Friday.
MetService meteorologist Mmathapelo Makgabutlane said earlier a cold front was expected to move on to the southern South Island tomorrow.
"There’s an element of uncertainty still in the forecast, but at the moment, it looks like there are some weather systems that could bring a risk of snowfall — possibly heavy snowfall.
"It is that time of year when the weather is quite changeable, and I think what we’re seeing with these weather systems is that lately we’ve had a lot of weather coming in from the west, but these weather systems are bringing in winds and colder air from the south, which is something we haven’t seen as often of late.
"It brings in that risk of snowfall, but it’s still early days yet at this stage."
She urged farmers in the middle of calving and lambing to keep up to date with the latest forecasts, so they could protect their newborns from frigid temperatures.
She said it was likely rainfall amounts tomorrow could reach warning criteria about northern and central Fiordland, and it was possible rainfall amounts could reach warning criteria about the main divide of the Southern Alps, southern Fiordland and inland parts of Southland and Otago.
"Snow may also develop to low levels about Southland and Otago, and there is low confidence that snowfall amounts could reach warning criteria above 400m about inland parts of Southland and Otago during the second part of the day.
"Additionally, there is also low confidence that northwesterlies could reach severe gale about the Canterbury High Country."
On Friday, there was still some uncertainty about the weather, but at this stage, the cold front looked like it may become slow-moving over the South Island, and many areas may get heavy rain or snow.
She said there was a possibility snow could fall to low levels about parts of inland Canterbury and Otago, and heavy snowfall was possible above 400m.
On Saturday, she said there was "considerable uncertainty" regarding the weather over New Zealand because an area of low pressure may move over the country.
That uncertainty would continue on Sunday, but at this stage fronts were likely to bring rain to many parts of the country, and cold southerlies may spread on to the South Island.
She said there was a possibility of snow to low levels about parts of Canterbury and Otago again, with heavy snowfall above 400m.
