"Really heavy'' show is on the way next week, followed by a sunny, calm spell.
Temperatures will get much colder by this weekend, MetService meteorologist Sarah Garlick said, with a heavy snow warning in place above 900 metres for the Central Plateau.
A belt of low pressure is currently bringing rain to much of the North Island, but "later on this week this low finally pushes away to the east and we get a good southerly change coming in late Saturday and during Sunday,'' Ms Garlick said.
That low was predicted to bring snow showers for the south and east of the South Island to fairly low levels as well as to Wellington, Wairarapa and low levels in the Central Plateau.
Snow in parts of the South Island next week would be "really heavy'', Ms Garlick said.
WeatherWatch.co.nz analyst Philip Duncan the cold snap could close the Desert Road but shouldn't last for more than a couple of days.
"It will be another 48 hour period with more wind and cold and snow on hills - but this isn't a major storm or anything like that, just another noticeable cold snap.''
The news would be welcomed by skiers and boarders - especially with sunny, calm, weather expected for many of our ski fields later next week, Mr Duncan said.
A high was forecast to move in late next week and last for at least a few days.
Mr Duncan said based on models by MetOcean and the Global Forecast System, cold southerlies were expected about mid-July.
"The prediction was that between July 9 and 13 the weather in New Zealand would significantly cool down following a very mild start to the month, with a cold southerly really pushing in around the 13th.''