The snow may be fast disappearing but freezing temperatures and black ice on the roads are still a reminder that winter is not yet over.
Weather Watch warned that it would be very cold tonight with temperatures dropping as low as -10degC in some areas in the lower and central South Island.
Head weather analyst Philip Duncan said severe frosts were expected in Southland, Otago and on the Central Plateau tonight.
With little wind and cloud, any warmth from the day disappeared at night and the coldest air sank down into the valleys, he said.
Snow melt and wet roads meant an extremely high risk of black ice on Friday morning and drivers in both the South and North Islands, especially those driving in valleys, were urged to be cautious.
Wellington and Gisborne were less likely to have frosts, due to frequent showers and brisk winds.
Heavy to severe frosts were expected from inland Taranaki to King Country and Waikato.
Meanwhile all the country's roads reopened today for the first time since the weekend.
