Thunderstorms, heavy rain, snow for Canterbury

Thunderstorms are expected for Canterbury, courtesy of an "unstable" cold air mass that could also bring snow, hail and heavy rain.

The MetService has issued a severe thunderstorm watch for the region including Christchurch, with storms possible from 3pm to 11pm on Tuesday.

The thunderstorms could also bring snow down to sea level, alongside 'large hail accumulations" and heavy rain, said the MetService.

The "unstable" cold mass will then make its way up north with snow expected on alpine passes.

Arthur's Pass is expected to have snow down to 600 metres with 3 to 6cms of snow on the roads.