It's a story of two islands for Sunday's weather, with heavy showers for Northland, Auckland, and Coromandel and severe inland frosts for most of the South Island.

MetService recorded the lowest temperature at Mount Cook, where the mercury plunged to -6.3C on Sunday morning.

Road snowfall warnings were also in force from the previous day, with NZ Transport Agency Waka Kotahi issuing a slew of them across both islands.

NZTA said snow and cold temperatures may cause ice to form on roads, making driving dangerous.

"Take extra care and remember to increase your following distance and be prepared for unexpected hazards when driving in these conditions," it warned.

MetService had no weather warnings in place on Sunday morning.

In a forecast issued at 6.18am, it said Northland, Auckland, and Coromandel could expect showers, some heavy, with squally thunderstorms possible about Northland and Great Barrier Island in the morning and afternoon.

For all the South Island, except Clutha, Southland and Fiordland, it forecast fine weather with severe inland frosts, and isolated showers about the Marlborough Sounds and Golden Bay clearing in the morning.