Tonight will mark the start to 48 hours of potentially violent winter weather to every region in the country as an Antarctic surge spreads northwards. The polar jet stream – which is the barrier between New Zealand’s temperate climate and the Antarctic cold – is shifting northwards and will envelop the entire country by Tuesday afternoon. “The front is moving into Southland right now and by evening or the early hours of Tuesday snow is expected in Invercargill, Queenstown, Cromwell, Alexandra and Dunedin. Thunder and hail will also be likely” says head weather analyst Philip Duncan. “Snow falls aren’t expected to be major in any populated places but the weather will still be harsh. By this Tuesday afternoon air from the Antarctic will be brushed over both islands with a wind chill below 10 degrees in all main centres”.

Last minute changes in wind directions now indicate sleet and bitterly cold rain will be in store for Canterbury.

But it’s not just about snow and windchill. Duncan says heavy and thundery showers are expected across the west coast of both islands with the risk of tornadoes. “We saw it last year and this year is no different, these isolated squalls are capable of producing small but deadly tornadoes. Our Weather Watch Centre is warning of a moderate risk of small, isolated, tornadoes within this system for 48 hours from Tuesday morning through to Thursday morning.   Auckland, Waikato, Taranaki and the West Coast will be most exposed to these thundery showers, other regions have a lower risk, such as Northland and Bay of Plenty . It can be sunny one minute, pouring the next. If you’re outdoors, keep a close eye on the sky”.

Meanwhile a low is expected to rapidly deepen over central New Zealand bringing gales to many areas during Wednesday and Thursday. “Snow on the Desert Road from tomorrow afternoon through to Wednesday morning, followed by gales over much of the North Island on Wednesday…motorists need to take extreme care. For motorists weather doesn’t get much more dangerous than this”.

Conditions should ease considerably on Thursday however another cold snap is expected late Friday in the South and everywhere else by Saturday.