Our first big spring storm will be on its way out over the next 48 hours, taking the heavy rain and thunderstorm threat with it.

What will replace the storm is a big ridge of high pressure that will build in off the Tasman Sea.  That will help establish a very potent southerly flow over the country, bringing some pretty chill air onto the South Island.

The air should be cold enough to send snow levels all the way down to sea level across Southland and Otago.  That means there is a chance for some snow, possibly heavy for the deep south, although significant snow accumulations below 500m aren’t likely.

There will also still be some strong and gusty winds in place, which will make things feel even colder thanks to the wind chill factor.  Highs on Tuesday and Wednesday will likely not make it out of the single digits in the deep south.

Also on Tuesday, sleet could spread north into Canterbury and Marlborough.  Government forecaster MetService says snow should remain above 200m in Canterbury and above 400m in Marlborough.  WeatherWatch.co.nz South Island forecaster Aaron Wilkinson says that he doesn’t see snow causing any issues in Christchurch on Tuesday.

Widespread frosts are likely in central Otago early Wednesday morning.  The rest of the Mainland could see frosts Thursday morning.

MetService is advising that these conditions could put a stress on livestock without shelter and make driving difficult, especially about the higher roads.  They are advising people in the south and east of the South Island to prepare for adverse conditions.

This cool down will also affect the North Island, but should warm significantly.  However, MetService feels there is a small chance for an accumulating snow over the North Island high country below 1000 metres on Wednesday.

By WeatherWatch.co.nz Analyst Howard Joseph