Subtropical airflows in the north meet subantarctic airflows in the south – this produces heavy snow at higher elevations, with miserable conditions for livestock (even at sea level due to the wet, cold, windy nature of the weather).

The low is not a storm – but the combination of low pressure plus two highs and the two air-masses meeting in the depths of winter means there are severe weather risks in both main islands…especially the South Island. At the other northern end of New Zealand temperatures will be up into the mid to possibly upper teens with a mixture of heavy rain, showers and large dry areas too in the milder northerly flow.

The much colder airflow works its way up the eastern side of the country this week, bringing colder, wetter and windier weather into the eastern North Island too (and a dusting of snow on the eastern ranges high up). But western parts of the North Island may not be so affected by the colder air.

Snow will be heavy in the South Island above 400 or 500 metres (and may go down to 300m or lower in some spots) and this may affect travel on highways and some airports due to snow and/or visibility issues. Otago, Southland and Canterbury are most exposed.

High pressure rolls in later this week and weekend and will bring frosts to sheltered areas.

See our newsfeed at WeatherWatch.co.nz or in our new App for more details, maps and links – it’s updated across Monday.

• WeatherWatch.co.nz