There's a cold blast coming this week with a chunk of the tropospheric polar vortex about to whip our way.

Temperatures are set to drop around mid-week, and there might even be snow.

In Te Waipounamu - the South Island - snow will be heaviest in Southland and Otago but it could fall to sea level in Ōtautahi Christchurch on Wednesday night, and even on the hills around Wellington.

Metservice meteorologist Lewis Ferris spoke to Māni Dunlop.