Weather: Biggest cold snap of 2018 so far to strike nationwide

New Zealand faces its first real taste of winter next week, as a nationwide cold snap comes early for the country.

Southerly winds will move over NZ this weekend, bringing cold air from the Southern Ocean.

"In true autumn style it's fairly short-lived but it's also one of the bigger cold snaps of the year so far with a big reduction in daytime highs coming, even for areas that have been summer-like lately," WeatherWatch says.

"Single-digit highs are possible next Tuesday through the South Island interior, with highs failing to reach the teens in a number of main centres and regions across the island.

"The North Island also feels the cool-down, with eastern areas tumbling as much as 13degC on where they were mid this week."

NIWA meteorologist Ben Noll says it will "sting a little bit more because of how warm it's been".

"When it does get cold we're going to feel it," he told Newshub.

"It's probably going to come with some wind and rain and snow likely in the peaks in the South Island."

MetService warns April temperatures are "set to take a tumble".

"Buckle in, we're in for a bumpy ride for April! The latest MetService long-range forecast is now up and it reeks of changeable weather, particularly for temperature," MetService says.

"As we move into next week, a couple of active fronts affect the country. Expect an unsettled period for both Islands, with respect to both precipitation and temperature swings," MetService says.

"A very cold southerly outbreak is indicated early next week, with potential for heavy snowfall, meaning that keeping up with the forecasts will be essential."