An "extensive polar blast" is predicted to cause widespread travel problems across New Zealand and drop snow in places that did not normally see it.
The storm was predicted to last until Wednesday.
"Our data has lined up for the first time all week and we're now ready to predict snow to sea level from Otago to Hawke's Bay," head weather analyst Philip Duncan said.
Duncan said data this morning, from the same source that accurately predicted snow in several main centres last month, called for snow to very low levels in Wellington and the Hutt Valley and the chance of snow in Napier, Hastings, Masterton, Dannevirke, Palmerston North, Hawera, Stratford and potentially Wanganui.
Snow was unlikely to settle for long to sea level, or near sea level, in the North Island.
Snow could cause travel issues for motorists right down to sea level in Wellington to Wairarapa, Hawke's Bay to Central Plateau, Canterbury to Marlborough, and Southland to Otago. Highways as far north as Gisborne could be affected.
Very heavy snow was predicted on the North Island mountain ranges. Snow showers were predicted for the Desert Road from Sunday night until Wednesday.
A very large southerly swell was expected in Cook Strait from Monday to Wednesday, potentially affecting ferry crossings.
"This snowstorm is really the perfect storm" Duncan said. "We have a high stretching over 6000 km from the tropics to Antarctica expected to form in the Tasman Sea, meanwhile a low in the central Tasman Sea will move east into the Pacific Ocean over the weekend, combining with a Southern Ocean low.
"All three systems will work together to provide an impressive southerly blast rarely seen here".
Farmers, who are in the middle of lambing season, have been advised to urgently move livestock.
Forecasters predicted the heaviest snow in southern and eastern regions of both islands, from Southland to East Cape.
Severe southerly gales were expected with wind chills bringing temperatures of well below zero.
