Warmer days ahead after one of the coldest mornings this year

After a chilly weekend, most of the country can defrost this week as temperatures start to rise.

But it's not all sunshine and rainbows as an incoming band of rain means some parts must brace for possible thunderstorms, especially in the South Island.

MetService said much of the country had their coldest morning of the year on Sunday morning and even Aucklanders woke to frost-coated lawns.

Overnight minimum air temperatures recorded in some airports were the coldest of the year including Auckland Airport (2.5°C), Christchurch Airport (-3.8°C), Taupo Airport (-4.2°C) and Mount Cook Airport (-11.5°C).

The coldest air temperature recorded in the country was -12.5°C at Lake Tekapo and in the North Island, temperatures plunged to -6.2°C around the central plateau.

This week will likely look different as MetService is forecasting temperatures to climb early this week with northwesterly winds strengthening.

Christchurch is expected to reach 17°C on Tuesday. Napier, Hastings, and Whanganui are also in for a toasty 19°C on Wednesday.

A heavy rain watch has been issued for the Westland Ranges and a strong wind watch for Canterbury High Country on Tuesday

MetService said rain is set to pile in from the west and winds to "squeeze over the spine of the Southern Alps."

"This week we see westerly winds bringing in waves of showers, so if you're looking for drier weather for the second week of the school holidays, the best bet is to travel east," MetService meteorologist Michael Pawley said.

MetService said a band of rain is expected to move up the West Coast on Monday and onto the North Island overnight.

There was a risk of thunderstorms with strong wind gusts for the South Island west of the main divide on Monday and Tuesday, and for Taranaki in the early hours of Tuesday morning.

Pawley said places like Hawke's Bay will likely get better weather this week.

"Canterbury will also get some fine breaks, but that big Nor'west Arch might be making an appearance."

The Nor'west Arch is a distinctive cloud that forms when northwest winds blow over the Southern Alps. The air is forced over the mountains, and cools as it rises and streams towards the east coast which forms a large white lenticular cloud, with a band of blue sky closer to the alps.