Aucklanders could still expect some showers into this evening after temperatures reached just 15C today, with a low of 11C.
"Things should be calming down a little bit overnight ... then tomorrow things will heat up again a little bit."
However, there was a moderate risk of thunderstorms in the afternoon, Ms LaBar said.
"For that we are looking at heavy rain, strong wind, gusts to 90km/h and some small hail with those showers. That's mainly in the afternoon, it should start to ease off by the evening."
Down south, temperatures plummeted overnight, with the coldest recorded temperature of -3C at Lake Tekapo.
There were still some showers this afternoon off the east coast around Banks Peninsula, Southland, and south Otago, Ms LaBar said.
She said it was "mainly fine conditions" over much of the rest of the South Island, which could mean some frost tonight, especially for those in inland areas.
After the South Island was blanketed in snow yesterday, those in the North Island got their first taste of the chill today.
Many Aucklanders had a rough night's sleep after thunderstorms arrived at 3.30am and continued until dawn, with squally gales and heavy downpours, WeatherWatch said.
Vector spokeswoman Sandy Hodge said there were a few small power outages about the Auckland area last night.
Seven customers in Waimauku, 120 in Muriwai Valley, 87 in Arapara near Port Albert, and 205 in western Mangere lost power due to the wild weather overnight, Ms Hodge said.
"While it was windy it wasn't sustained winds over 60km/h which is normally what would cause the problem. It was cold, yes, but that doesn't normally effect us so much.
"It was a little bit blustery but not too bad."
Jackets and winter woollies were being pulled out across the Bay of Plenty as the trough of low pressure dragged up cold air from Antarctica.
MetService said Tauranga would reach a high of 17C, but warned people to get winter duvets ready for an overnight low of 6C.
The polar blast also brought an early snowfall to fields in both the North and South Islands, leaving skiers hopeful for a good season this winter.
Staff at Cardrona Alpine Resort and Mt Ruapehu have had two dumps of snow in as many days as the chilly southwesterly moved up the country.
"We've received a good 10cm-15cm of snow at our bases at each ski area, Whakapapa and Turoa," said Simon Dickson, executive manager commercial at Mt Ruapehu.
The early snowfall was "promising" for the season ahead, he said.
"We always get a good one or two snowfalls like this in April and early May, so it's just a nice reminder that Mother Nature's at work and we're on the back of that blast that's giving the South Island and our ski fields colleagues down there a bit of a dump of snow as well."
At the Cardrona resort near Wanaka, "pretty good" snow drifts of between 50cm and 70cm had accumulated yesterday on the mountain.
"It's really good at this time of the year, more for marketing than anything else," said Adam Wilson, from the resort's sales and marketing department.
"It gets people interested in the ski season. A lot of people are thinking about it at this stage anyway, but especially over in Australia seeing all of these snow images definitely makes them think, 'we're in for a good ski season'."
Meanwhile, those in the Hawkes Bay escaped much of a cold snap.
Rainfall throughout the region in the 24 hours to early last night was mainly less than 10mm and, while temperatures had dropped from those on Sunday -- when Napier's 23.3C was the day's highest maximum recorded by MetService -- some "recovery" was expected from later today, a spokesman from MetService said.