Clashes of warm and cold air sparked thunder and over 200 lightning strikes around eastern parts of central New Zealand this afternoon.
MetService severe weather forecaster Eric Brenstrum said such events happened in spring when the sun was warming the ground but conditions could still present chilly air.
Mr Brenstrum said the storms were sparked by cold air moving over warm ground, causing the warm air near the ground to rapidly rise and expand.
Processes then occurred which led to turbulent conditions.
"You get an enormous electric potential across a short piece of air. The air then ionises and becomes a conductor and you get lightning."
Mr Brenstrum said there had also been hail in the Wellington area, including reports of hailstones 1cm across in the suburb of Johnsonville.
There were similar conditions this morning in Canterbury, where snow recently fell to low levels.
After heading north through Marlborough and Wellington, the stormy conditions continued through parts of Wairarapa.
Mr Brenstrum said probably the most concerning outcome of the weather at present was that severe frosts were expected across much of the country tomorrow morning and on Sunday.
The frosts left vineyard owners and orchardists in Otago, Canterbury, Marlborough and Hawke's Bay exposed to potential damage to tender young fruit.
Hundreds of helicopters were expected to be on standby so pilots could fly them over vulnerable crops to push down warmer inversion layers and prevent frost from settling.
