Heavy snowfalls in South Canterbury and Otago have closed roads, and forecasters warn power cuts and flooding could be ahead for many areas.
The Lewis and Porters passes are both closed, as is State Highway 7 between Springs Junction and Reefton, blocking the major routes between the east and west coasts.
Snow also closed the road between Te Anau and Milford this afternoon, and as a precaution the highway connecting Kyeburn and Outram northwest of Dunedin was shut too.
There is also a severe thunderstorm watch in place for western parts of central New Zealand, including New Plymouth, Hamilton, Whanganui and Palmerston North. Nelson and Westport in the upper South Island have also been put on alert.
MetService's Peter Little said the storm is a complex system with a slow-moving series of cold fronts interacting with a strong jet stream in the atmosphere and warmer air to the north.
"There has been quite a lot of thunderstorm activity about the west of the South Island, the Buller region in particular has seen a lot of thunderstorms. There's been some rainfall on the West Coast and also in the east for Canterbury.
"For those places inland, it's falling as snow above about 300 or 400 metres, at the moment the most snow we've seen has been at Arthur's Pass, they've had quite a decent dumping of snow there, certainly a few tens of centimetres."
Mr Little said there had been some snow on the Crown Range and Lindis Pass in Otago overnight and more was expected. At 9am today the temperature at the top of the Crown Range Road was -1.4C.
Happy Saturday ❄️— NIWA Weather (@NiwaWeather) August 9, 2019
Forecast snowfall through Sunday morning, mainly accumulating over 300 m.
⛓️Travel to the conditions and check with
NZTA for any potential road closures.
More on today's weather: https://t.co/hViIi4WNKD@nzta_news pic.twitter.com/SSgd4Jp4rT
But he said heavier dumps today could bring as much as 40cm of snow in areas above 500m and snow warning are in place for areas above 300m.
The highway between Dunedin and Waitati was forecast to receive up to three centimetres between this afternoon and early tomorrow morning.
Low pressure from the Tasman Sea is heading towards #NZ this weekend. Severe Weather Warnings and Watches have just been issued for snow as low as 300 metres for Canterbury and Otago. Heaviest snow above 500 metres. Get the details: https://t.co/qHyE5zhh6X ^CRN pic.twitter.com/iCtA8gVPrO— MetService (@MetService) August 8, 2019
Mr Little said the heavy snow today could be enough to damage powerlines and trees, and could disrupt many roads and highways.
"With snowfall, if it falls on to trees it can make the tree branches heavy, these can then fall on to powerlines and causes outages, so people should be prepared in those parts of the country where we are forecasting snow and if travelling they'll need to take care on the roads."
The heaviest falls this morning were at Porter's Pass and Arthur's Pass.
State Highway 73 from Springfield to Arthurs Pass (Porter's Pass) is closed due to snow. The SH73 route to Otira has also been closed. Motorists are being advised to take extra care though the area and plan ahead.
UPDATE 9:10AM— NZTA Canterbury/WC (@NZTACWC) August 9, 2019
Due to snow, SH73 from Springfield to Arthurs Pass ((Porter's Pass) is now CLOSED. Please note SH 73 from Arthurs Pass to Otira remains CLOSED to towing vehicles, Chains essential. Please take extra care though the area and plan ahead. ^EHhttps://t.co/9MkM3mX2ik
WEST COAST - SNOW - 8AM— NZTA Canterbury/WC (@NZTACWC) August 9, 2019
Snow and ice are impacting SH73 in West Coast, Please note:
• SH 73 Arthurs Pass to Otira - Snow - CLOSED to towing vehicles, Chains essential.
• SH 73 Springfield to Arthurs Pass (Porter's Pass) - Snow - CLOSED to towing vehicles, Chains essential. ^EH pic.twitter.com/YjGUjGQUJm
The Transport Agency said snow, ice and heavy rain is making driving very treacherous in areas.
Journeys manager Tresca Forrester said it did not look like it would improve any time soon.
"Snow has closed State Highway 73 through the Porter's Pass from this morning, State Highway 7 through the Lewis Pass, further road closures are possible for north Otago and Canterbury throughout the day as the weather sets in.
"Chains may be essential on some roads, we've got heavy rain and ice and snow across many parts of the highways this afternoon."
The director of Civil Defence and Emergency Management for Otago, Chris Hawker, said the situation was being closely monitored for travel and access to areas, but no weather responses were being activated at this point.
"We've been very fortunate this winter because it's been an extremely mild one, so it's obviously a little bit more of a shock when it does arrive," he said.
Severe weather warnings and watches were issued yesterday as low pressure from the Tasman Sea headed towards the country.
Rain is expected in many areas of the North Island this afternoon, with flooding in parts expected.
Heavy rain today caused some surface flooding in Wellington's south coast and the city councils said Island Bay was blanketed with hail this afternoon - something very unusual for the area.
State Highway 2 Waimana Gorge is likely to remain closed this weekend due to the prospect of heavy rain in the Bay of Plenty.
MetService said the North Island should expect more thunderstorms tomorrow, and Canterbury and Otago will have rain and snow in the morning but it is forecast to ease.