"That extra 20kmh over the limit is only going to get you to the next car ahead of you faster," Senior Sergeant Craig Dinnissen said.
"Passing lanes aren't drag strips.
"We don't want to be telling your loved ones you aren't coming home again."
Murky and rainy conditions in some parts of the South and the large number of motorcycles on the roads for the Brass Monkey Rally could create a perfect storm for crashes, and police would be out in force this weekend, Snr Sgt Dinnissen said.
"Plan for a long trip home.
"If you're running late, just be late."
Heavy rain overnight kept emergency services busy with callouts for minor flooding in north Canterbury towns, RNZ reports
MetService issued a warning of significant snow and rain for parts of Canterbury and Marlborough until Saturday morning.
Heavy snow is also possible above 400 metres.
Canterbury fire services said they had 25 weather-related calls overnight for minor flooding in the North Canterbury towns of Woodend, Kaiapoi and Rangiora.
Gales were forecast for central and northern New Zealand until Saturday morning.
The NZ Transport Agency is warning motorists to take care on the Remutaka Hill (State Highway 2) north of Wellington because of strong wind.
Meanwhile, MetService recorded more than 600 lightning strikes across the country overnight.
Duty forecaster Larissa Marintchenko said the areas most affected were Whanganui-Manawatu, Kapiti Coast and Auckland.
The thunderstorms, which came off the Tasman Sea at around 7pm yesterday, pelted West Auckland with larger than normal hail.
In the past 12 hours, MetService has recorded 5mm to 7mm of rainfall across the Auckland region. Some areas recorded up to 15mm.
However, that's nothing compared to the Canterbury region which had 50mm of rainfall in the past 12 hours.
More isolated thunderstorms and hail are possible over the next 24 hours in Auckland and in most main centres across New Zealand as the main polar blast moves in.
Marintchenko said temperatures were expected to drop to new lows below 0C tonight in the South Island.
Last night temperatures dropped to 4C in the South Island and 10C in the North Island, she said.
In the South Island, Cardrona Alpine Resort has officially opened its doors but at this stage only for gondola rides and sledging.
It is expected to be open to skiers and snowboarders later in the week when the new snow has been groomed.
Cardrona Alpine Resort communications executive Jen Houltham said they had 10cm of new snow last night and it was still falling this morning.
"It's like winter has just flicked on the switch."
- additional reporting RNZ and NZME
