A potent second winter storm is looming with school holidays ending in wild weather that threatens havoc across New Zealand.

Tomorrow will take a turn for the worse with 48 hours of snow, heavy rain and gales set to lash the entire country.

Travel in both islands is expected to be thrown into chaos with roads inundated by flooding and wild winds damaging property and making driving hazardous. Snow is also likely to pose problems on higher roads and with livestock across Canterbury and North Otago.

MetService today issued a swathe of weather watches for the upper half of the North Island and eastern regions of the South Island.

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Forecaster Tom Adams said Canterbury was set to be slammed in the coming storm with some parts potentially getting a month's worth of rain in just 24 hours.

"At the moment what we can say with high certainty is that there is going to be a lot of rain that will reach warning criteria," said Adams.

The North Island was in the firing line as well with heavy rain and gales for the Bay of Plenty across to Taranaki north on Thursday and Friday. Central regions, still recovering from last week's snowstorm, would be pummelled for the second week running.

The rain and strong winds would start spreading across both islands on Thursday.

The south would then shiver through another cold snap with significant amounts of snow falling to 300m in Canterbury and southern Marlborough and 500m across North Otago on Friday.

As well severe southerly gales were expected to howl through coastal Canterbury and the Kaikoura coast during Friday and early Saturday.

In the North Island heavy rain is expected to fall across the upper half for the next two days with gales battering eastern and northern regions for the coming three days.