The MetService is urging motorists in the South Island and Desert Rd to take care as a cold southerly brings snow down to 500m in places.
While the dusting - between 5cm and 10cm - won't arrive in the North Island until the early hours of tomorrow, the MetService says temperatures are currently quickly switching from mild to cold as the southerly makes its way up from the bottom of the South Island.
Duty meteorologist Peter Little says the front has just hit Christchurch which has already reached its high temperature of 13C for the day, and is currently sitting on 11C, but it will plummet well into single digits this afternoon.
"The southerly that we've got moving northwards is currently over the South Island approaching Christchurch, that's going to see a return of some cooler temperatures and also bringing some snow with it."
The unusually warm June temperatures - where Auckland's 19.9C was one of its highest June temperatures recorded - are now coming to an abrupt halt with temperatures due to plunge overnight.
"Now we're getting a cold front move northwards and that's followed by cooler southerlies so that's going to see temperatures plummet more to what we expect in winter levels. Over the lower South Island will be single digit maximums and those temperatures over the North Island which we have seen in the high teens or early 20s as the southerly blows through tomorrow they will be more early to mid teens. So it will be a much, much cooler day tomorrow with southwesterlies across the North Island."
Road snowfall warnings were now in place for the Desert Rd with snow showers expected from midnight until 7am tomorrow. Snowfalls between 1cm and 3cm are expected to accumulate near the summit with lesser amounts down to 900m.
However, up to 5cm is expected on the Lewis Pass, State Highway 7, between 1pm and 6pm today, with lesser amounts down to about 500m.
The snow showers have already begun this morning on Porters Pass, State Highway 73, and will continue until about 4pm, while Arthurs Pass will continue receive dustings of about 2cm or 3cm until about 5pm.
Dustings are also expected on Milford Rd, State Highway 94, south of Lake Gunn before spreading elsewhere as the winds turn more westerly.
"The lower South Island is going to struggle to get into double digits. Dunedin is currently 8 degrees and it's probably not going to get a lot warmer than that."
However, there was some good news on the horizon as a ridge of high pressure makes its way towards the country.
"So for the South Island, especially where that ridge pushes on first, that's going to mean clear skies and the winds are going to drop away and inland places will likely see some fairly severe frosts down to about -6 in places. It's certainly going to get pretty cold. You'll need to rug up."