Make the most of today’s sunshine - the weather is about to turn wet and wild for the next couple of days in the South Island.
Then tomorrow, a front preceded by a strong moist northeasterly flow would move slowly east on to New Zealand, he said.
"Wednesday and Thursday are the main risk period for severe weather, and heavy rain watches are already in force for western and northern parts of the South Island."
There was a chance of warning amounts of rain over a large part of the South Island, including Southland and the headwaters of the Canterbury and Otago lakes and rivers.
"It’s likely some of these will be upgraded to orange warnings and areas in the North Island may be added."
A heavy snow watch for Central Otago and Queenstown Lakes was confirmed this morning for 12 hours from 9am on Wednesday.
Periods of heavy snow above 700m are expected, where snowfall amounts may approach warning criteria.
MetService meteorologist Mathapelo Makabulane said the snow could hit the southern mountain passes.
"We are still in snow season and we see the return of some snowfall in the Otago region, Southern Lakes into parts of Central Otago," she said.
"If people are going to be travelling on those high level roads, places like the Haast Pass, Lindis Pass, Crown Range Road, we could see some snow settling on those roads."
Road snowfall warnings have been for the Crown Range Rd, Milford Rd (SH94), Lindis Pass (SH8) and Haast Pass (SH6).
The unseasonable wintry conditions are likely to stress livestock and bring travel disruptions.
NZ Transport Agency Waka Kotahi said that given the school holidays were under way, drivers needed to take extra care as roads would be busy.
“It is essential people drive to the conditions and be prepared for hazards on the road,” said NZTA Journey Manager Tresca Forrester.
The Milford Road will close at 5pm today owing to an increased avalanche risk. With more rain and snow in the forecast it may remain closed on Wednesday, NZTA said.
Ferris said the "potentially severe weather" was brought about by a low pressure system approaching from the Tasman Sea, "which drags some warm and humid air across our shores".
"While this does mean some warmer than average temperatures, it also increases the chance of heavy rain as the system passes over.
"Strong northeasterly winds will also be seen before the rain arrives."
On Thursday, an area of low pressure and associated fronts would direct that moist northeasterly flow on to much of the country, and rainfall could reach warning amounts in Dunedin, North Otago,Clutha and Southland.
Again, snow could possibly fall to 500m in inland Otago and the south of the Canterbury high country in the morning.
On Friday, a slow-moving front and a moist easterly flow were expected to bring more rain to the southeast of the South Island.
"Prolonged rain is also possible around these areas and severe weather forecasts might be issued", Mr Lewis said.
The rain was expected to ease on Saturday.
While it was still too early to say if the heavy rainfall would cause any flooding, Emergency Management Otago stakeholder engagement adviser Erica Andrews said the organisation would be keeping a close eye on the situation.
- additional reporting RNZ
