Don't pack away your winter wardrobe just yet - this week's warm weather could be out in the cold by Monday.

Forecasters say while most of the nation should enjoy a sunny Saturday, a nasty southerly will creep up the country from this afternoon.

Weather Watch's Philip Duncan said rain and cooler temperatures would be across the whole South Island by the end of Sunday, and in the north by Monday.

"Rain will push in across both main islands with even the driest parts of New Zealand enjoying some rain," he said.

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The rest of next week would likely be rainy and cold as well.

MetService rain radar shows showers just in time for work at 7am on Monday. Photo / Supplied
MetService rain radar shows showers just in time for work at 7am on Monday. Photo / Supplied

The MetService said the change was brought on by a "broad complex trough" moving east over the country.

"Low centres are expected to develop east of the country during Monday and remain slow moving through to Wednesday," it said.

"Outbreaks of rain, showers, even hail, are expected over much of the country during this period, with the more persistent rain likely about eastern parts of the South Island, possibly reaching the lower North Island on Wednesday."

It said while the weekend would be warm, with highs in the early 20s for most of the North Island, temperatures would be "noticeably" colder next week.

"Snow is expected about eastern parts of the South Island above 400 to 500 metres, and possibly about the North Island high country above 1000 metres," it said.