Winter is tightening its grip on the region with the onset of freezing temperatures, snowfall, heavy frosts and black ice -- and a cautionary message to motorists. forecaster Philip Duncan said there was a chance of black ice on rural roads this morning, particularly inland.

"Sheltered valleys in more rural areas are the perfect places to find black ice."

The warnings come after overnight temperatures plummeted in the region this week.


Mr Duncan said temperatures on parts of the Napier-Taupo highway fell as low as -6C yesterday morning and there were reports of widespread frost, as well as snow on the Ruahine Ranges.

A Te Pohue resident told Hawke's Bay Today the town had experienced heavy frost yesterday morning. She had measured the temperature at -2C and it had taken her half an hour to defrost her car.

"It was all white outside ... it was the coldest it's been this year."

Norsewood-based author and hobby farmer Lyn McConchie said it was -3C on her lifestyle block yesterday morning.

"There was a skin of ice on the geese's water trough, and they had something to say about it."

MetService meteorologist Liz Walsh said Hastings' overnight low had hovered around 0C for the last two nights while Napier was around 1C.

Ms Walsh said a cold southerly flow was responsible for snow on the region's mountain ranges yesterday morning.

Any showers above the Ruahine and Kaweka Ranges had fallen as snow, as the temperature 1000 metres above sea level was below freezing.

Mr Duncan said there was a chance of more snowfall on higher ground later this week.

Ms Walsh said clear skies, cold air and a lack of wind were the contributing causes to frosty weather this week.

"If the road is wet and it frosts over, that can lead to black ice."

Other parts of the country, particularly the South Island, also felt winter's icy grip.

A number of road accidents happened in Dunedin yesterday due to black ice, Ms Walsh said.

Federated Farmers' Hawke's Bay president Will Foley said frosts hadn't had an adverse effect on stock because frosty mornings were followed by fine, warm days. Frost slowed grass growth and thereby affected the amount of feed for stock, but rainfall in April and mild, moist conditions had caused an abundance of grass growth this autumn, Mr Foley said.

"It's been warm, mild weather which equals excellent grass growth, so farmers are in a pretty happy state."

Mr Duncan said a warm northwesterly would bring a brief respite from colder temperatures tonight and tomorrow.

However, Friday would see a cold southerly change lowering daytime highs by as much as 6C, he said.

A predicted daytime high of 17C tomorrow could drop to as low as 12C on Friday.

The southerly would die out on Saturday, with warm weather creeping back in time for the weekend, but frost would persist early next week.

Sunday, June 1, was the official start of winter, Mr Duncan said.

Eastern District Command Centre Senior Sergeant Ross Smith said anyone driving in the early hours of the morning in areas prone to black ice, such as those sheltered from sunshine, should exercise extreme caution.