"There is a surge of colder air heading our way. It's going to feel pretty cold," said MetService meteorologist Tom Adams.
The cold snap wouldn't match the polar blast that left the country shivering at the start of May, but snow was on its way to parts of the South Island today, particularly in higher places.
Snow showers could affect higher South Island roads today, and road snowfall warnings may be issued, MetService warned.
Parts of Otago was already feeling the chill with temperatures hovering just above zero early today. Motorists were warned to beware of slippery roads as rain-soaked surfaces turned to ice.
Parts of the middle of the North Island, such as Mt Ruapehu, could expect white peaks by tomorrow, Adams said.
Auckland tomorrow was looking to reach a high of 15C and an overnight low of 7C and Wellington was forecast to be a few degrees colder with a 12C high and an overnight low of 5C.
Invercargill was unlikely to break double figures tomorrow and an overnight temperature forecast at 2C to 3C, Adams said.
And Queenstown would drop below freezing overnight tomorrow.
"You'll be getting a cold southerly blast."
In northern Westland and Buller, rain may be heavy enough to reach warning criteria, MetService forecast.
Rain in the area was forecast for today and was likely to get heavier through to tomorrow.
Today and tomorrow, southwest gales were predicted about southern Fiordland and coastal parts of Southland, Clutha and Dunedin, possibly becoming severe around Nelson.
In the North Island, severe west-to-northwest gales were likely about Wairarapa and Hawke's Bay south of Hastings.
Today's MetService forecasts:
Auckland: Showers becoming heavier tonight. High of 17.
Hamilton: Showers, becoming heavier this afternoon. High of 17.
Wellington: Cloudy, occasional showers. Gale NW. High 15.
Christchurch: Cloudy, afternoon rain, strong SW easing. High of 15.
Dunedin: Rain at midday with strong cold SW change. Evening showers. High of 10.
