After a warm, wet, and unsettled weekend, MetService is forecasting an abrupt midweek plunge in temperatures.

High temperatures cling on today and most of Tuesday as a pulse of warmer air from the northwest washes over Aotearoa, with many centres expecting overnight temperatures in the mid to high teens.

However, a cold southerly change spreads up the South Island on Tuesday, and over the North Island on Wednesday.

'The difference will be most notable in the South Island, with a few locations set to see around a ten degree drop in temperature,” says MetService meteorologist Alwyn Bakker.

'In particular, Christchurch is expected to reach 24C on Tuesday, just ahead of the change, but only 11C on Wednesday.”

For the North Island, daytime temperatures will decrease less dramatically, but it's the overnight temperatures that will be taking the hit. Auckland will be going from a muggy 16C on Tuesday night to a mild 8C on Wednesday night.

As the southerly change moves over the county, it brings snow to parts of the South Island.

The snow is expected to lower to 600 metres in Southland, Dunedin, and the Southern Lakes from Tuesday afternoon, and to 700 metres at night in the Canterbury High Country. Road Snowfall Warnings have been issued for high level roads in the areas.

Heavy Rain Watches and Warnings for Tuesday and early Wednesday have been issued for parts of the west coast of the South Island, and for Mount Taranaki and the Tararua Range, and Strong Wind Watches for parts of the Canterbury High Country, Marlborough, Wellington and the Wairarapa.

'We advise people to check MetService.com to keep up to date with the latest forecasts, as we may upgrade parts of the watches to Orange Warnings or add further areas as the situation develops,” Bakker cautions.