Snow is forecast to fall in Southland, Canterbury, parts of central Otago and Dunedin's hillside suburbs.
Clark says it is too early to tell how much snow would fall.
But everywhere would notice the sudden cold snap as temperatures start to spiral downwards on Thursday.
Before the snow, though, rain and wind would hit parts of New Zealand. Regions on the western coasts of both islands are expected to bear the brunt of the wet weather.
A number of watches and warnings have been issued today ahead of the coming deluge.
The worst weather is expected to hit the Far North and Nelson from tonight.
However much of the upper half of the North Island and West Coast of the South Island have also been put on notice with forecasters warning it could easily worsen.
This would be followed by a couple of days of bitterly cold weather as snow and sleet covered the lower South Island.
Snow is expected to start falling in Queenstown and Alexandra on Friday. Temperatures were set to plummet to single digit highs of just 7C this weekend.
Weatherwatch.co.nz said daytime highs at the warmest point on Friday and Saturday might only reach 4C to 6C for many southern centres.
Coupled with wind chill temperatures would probably plunge to below freezing at times in Southland and Otago, the two regions most exposed to the blast.
Clark said everywhere would notice the sudden wintry change as the air laced with an icy chill enveloped the country.
