The MetService has issued a heavy rain warning for the headwaters of our lakes from 1am Thursday (September 21) to 2am Friday (September 22), and a heavy snow watch is in place.

An active front, preceded by moist, gale to severe gale northwesterlies, is expected to move north over the South Island during Thursday and Friday and warnings and watches are in place for much of the island for heavy rain and strong winds.

Expect 200 to 350 mm of rain about the main divide, and 100 to 150 mm within 30 km farther east. Peak rates of 15 to 25 mm/h, and possible thunderstorms.

The MetService says there are uncertainties with the movement of the rainband on Thursday and into Friday, therefore the timing and the total amounts may change.

Rain is expected to turn to snow above 500 metres from 9am to midnight Friday with heavy snowfall possible above 700 metres affecting the Crown Range Road and possibly other alpine passes.

Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.