The unusually cold temperatures that have affected New Zealand over the past few days should return to normal for most places this weekend.

A stronger westerly flow developing over the country should mix in some slightly warmer air, and also push cloud and a few showers into western areas and the far south.

Unseasonal cold mornings have been experienced in the Bay this week.

"It's not going to be warm, but it will be warmer than what it has been!" says MetService meteorologist Stephen Glassey.

The Bay of Plenty will see an overnight low of four tonight before temperatures head back to around the nine degree mark.

Daily highs are expected to be around 15-16 degrees.

Earlier this week, frosts were reported right across New Zealand this week, including Northland and Auckland.

South Island's Mackenzie Country in particular has experienced bone-chilling temperatures.

Pukaki Aerodrome near Twizel dropped to minus 19.8 degrees on Tuesday morning, and Omarama dipped to minus 21 degrees on Wednesday morning.

Although these were records for these places, they fell short of reaching the New Zealand record of minus 25.6C at Ranfurly in 1903. The freezing temperatures in the Mackenzie Country were due to a combination of several factors.

Firstly, a very cold southerly flow died out over the South Island on Monday. This left behind clear skies, no wind and snow covered ground, providing perfect conditions for temperatures to plummet.

Proximity to the winter solstice, providing the longest nights of the year, also helped.

"Although the cold air might stay trapped in the Mackenzie Basin for a little while longer, it shouldn't reach the same extremes as the past few nights due to the westerly flow developing over New Zealand," says Stephen.

Looking ahead to the weekend, this westerly flow should bring fine weather for the Super 15 semi-final between the Hurricanes and the Brumbies in Wellington on Saturday night.

Kick off temperature is estimated to be around 10 degrees with a northerly breeze.

Fine weather is also forecast for the second semi-final between the Highlanders and Warratahs in Sydney later that evening.