Bad news for sky-gazers - thick cloud across the country means there is little chance of witnessing the rare transit of Venus phenomenon tomorrow.

Meanwhile the South Island is on track for the heaviest dumping of snow this year, with 50-100cm possible in parts of North Canterbury.

A deep low is approaching New Zealand today and will cross the country tomorrow night.

Rainbands associated with the low will spread across both islands, the MetService forecasts, with very cold air set to move over the South Island.


MetService spokesman Daniel Corbett said the weather system over the country will make viewing the transit of Venus unlikely for most of the country.

The rare event will be visible in New Zealand from 10.15am to 4.43pm tomorrow.

The transit of Venus sees the planet slide slowly along the face of the sun over six hours.

It was last seen in 2004 and will not be visible again until 2117.

"Throw it out of the window - there is no chance," Mr Corbett said.

"The best chance, or at least better chance ... would be heading further south, somewhere like Mt John or maybe further south into the likes of inland Otago and inland parts of Southland, where you are away from that system.

"The North Island will be very tricky, because we will have this area of moisture, and there will be a lot of left-over cloud - maybe you could try pick out the East Coast, perhaps Gisborne ... but that's just a low chance there.

"You'd prefer to have a big ridge of high pressure and clear skies, but unfortunately that's not what we've got.


"So we'll just have to keep our fingers crossed and maybe do some anti-cloud dances."

Heavy rain warnings are in place for the eastern ranges of the Bay of Plenty, Gisborne north of Ruatoria, northwest Nelson, Buller and Westland. Heavy snow warnings are in place for Canterbury, Marlborough south of Seddon, while strong wind warnings are in place for southern Taranaki, Wanganui, Taihape, Gisborne, northern Hawke's Bay, Wellington, Wairarapa and the Marlborough Sounds.

Much of the South Island will see snow falls today, but the heaviest are expected about North Canterbury. Above 300-400 metres, 50-100cm of snowfall is possible, Mr Corbett said, with 10-20cm possible down to 100m above sea level.

"We start seeing a front spread its way north later today. So it will bring a little bit of snow down to the likes of Southland, Otago, but the main battleground is going to be across parts of Canterbury, North Canterbury, over towards inland Marlborough, [stretching from] north of Rangitata River towards south of Seddon," Mr Corbett said.

"We're getting moisture over the Tasman Sea coinciding with very cold air from the South Ocean and where the two are meeting is where will have trouble."