MetService has issued a Severe Weather Outlook for the week ahead.

"On Tuesday, a strong northwest flow covers the country, north of a low that is expected to pass just south of the South Island," says a MetService spokesperson.

"This will bring gale west to northwest winds in many places and heavy rain to the west of the South Island and southern North Island."

MetService says there is moderate confidence that a rainfall warning will be needed in Fiordland and Westland during Tuesday.

"Confidence is low that a rain warning will be needed in Buller and the Canterbury high-country on Tuesday and about the Tararua Range on Tuesday and Wednesday."

There is moderate confidence that west to northwest winds could rise to severe gale in exposed places in the east of New Zealand from Southland to Wairarapa, including Wellington during Tuesday.

"Note, late Tuesday in the south of the South Island, the flow should turn west to southwest, but could still be severe gale in exposed places."

Overnight Tuesday to Wednesday, snow may fall to reasonably low levels in the south of the South Island, and there is low confidence that a snow warning will be issued for inland areas of Southland, Otago and South Canterbury for heavy snow above about 500 metres.

"Computer models are still very uncertain about the level of heavy snow, and the snow level may change closer to the event."

On Wednesday, winds turn southwest over the country as the low moves away. There is low confidence that severe gale westerlies will be experienced in Central Hawke's Bay on Tuesday and Wednesday and that severe gale southwesterlies will affect Northland and Auckland on Wednesday.

About Tairawhiti/Gisborne and northern Hawke's Bay there is low confidence that severe gale southwesterlies will affect coastal areas during Wednesday and Thursday. During the same time, there is also low confidence that a rain warning will be needed in these areas, most likely inland.

The southwest flow should ease over the country during Thursday and Friday as a large high over the Tasman Sea moves onto New Zealand.