MetService head of weather news Heather Keats said two sections of State Highway in the Mackenzie Country that were closed overnight Saturday - because of risk from snow and ice - had reopened by Sunday morning.
The New Zealand Transport Agency said the crews had been busy gritting and treating areas of ice on the roads.
Keats said there are still a couple of road snowfall warnings in place for Lewis Pass and Porters Pass until about 9am this morning,
"There's been quite a bit of rain that's pushed in over the Canterbury region overnight so Port Hills has had some snow again and today it'll be to about 700m but definitely easing as those showers clear out of the South Island today," she said.
She said people would have noticed that today is a couple of degrees warmer than Sunday in places like Wellington and Dunedin.
"It is starting to feel a little warmer and it will continue to warm back to average today and tomorrow and then even slightly above average for the North Island as we head into the week," she said.
The coldest place in New Zealand this morning was Mt Hutt at -7degC, while Manapouri Airport in Te Anau recorded -4 degrees.
Keats also said the big wells in Cook Strait will ease, but warned a new weather rain system could hit mid-week.
"We've got a new big deep low pressure system out over the Tasman and that's actually starting to influence our weather from today heading into this week and that's going to see the next bout of rain the next large swells and we can expect pretty unsettled kind of week from about Wednesday."
Thunderstorms rock North Island
Much of the upper North Island have been rocked by thunderstorms overnight, with over 3000 lightning strikes recorded.
Kaipara Harbour was hit most, with Auckland also berated by loud bangs throughout the early morning hours on Monday.
Residents in Helensville also reported hail.
Keats said the loud thunder even gave her moment for pause.
"It scared the bejesus out of me," she said.
"I don't think many people in Auckland would have slept through their alarm this morning, that's for sure.
"There's quite a few of those little sparks up over Auckland at the moment. These squally thunderstorms are going to continue to kind of roll over the city like they did last night."
Keats said the majority of the lightning strikes was over central Kaipara Harbour, but a few were seen in the Auckland region too.
A couple of storms have bubbled up over the city but will slowly head out offshore and clear in Auckland and the Upper North Island throughout the morning, she said.
"It's been a pretty unstable couple of days with one weather system kind of pushing in that westerly flow over the Upper North but we still have that biting southerly coming up from the south that's been responsible for the cold temperatures and the snow," she said.
Keats advised morning commuters and parents dropping off their children at school to keep an eye on the rain radar, with strong winds and heavy rain expected until about 9am.
