Canterbury faces a cold, unsettled spell, with thunderstorms and small hail possible on Thursday, snow forecast to lower to about 800 metres on Friday, and clearer skies returning on Saturday.

MetService’s Thursday morning thunderstorm outlook places the area from about Banks Peninsula northwards to Wairarapa at moderate risk during the afternoon and evening. Any thunderstorms developing could bring small hail and bursts of heavy rain, with intensities of up to 15mm an hour.

The risk comes as cold, unstable air follows a front tracking north through the South Island. As colder air spreads overhead, conditions will become favourable for thunderstorms across parts of eastern and western South Island, with a lower risk outside the identified moderate-risk area.

Across Canterbury, Thursday’s early rain is expected to give way to showers, becoming heavy and potentially thundery during the afternoon and early evening. Showers should become confined to Banks Peninsula by evening.

Northwesterly winds will turn southwesterly during the morning, with daytime temperatures ranging from about 9C to 14C depending on location. Overnight temperatures are expected to fall to around 1C or 2C.

Friday will bring another round of unsettled weather. Isolated showers are forecast to become more widespread during the morning and afternoon, although there will also be fine intervals.

Snow is expected to lower to about 800 metres later in the day, bringing a wintry change to higher parts of the region. Northwesterlies will again shift southwesterly during the morning.

Friday’s forecast highs range from about 11C to 17C across the area, with overnight temperatures falling to between minus 2C and 2C.

Conditions are expected to improve on Saturday, with generally fine weather and mostly clear skies. Winds will tend northerly by the afternoon, with a high near 13C and overnight temperatures around minus 2C in colder areas.