Sub-tropical air in the North Island is being flushed out by a strengthening north westerly flow ahead of an Antarctic change moving in.
The air flow is a bit complicated, bending and twisting from Antarctica to reach New Zealand, and getting sucked around low pressure over us – the more direct the airflow the colder it is.
Polar air is now feeding into the lower South Island and is getting into the mix further north – but as you can see Canterbury is the boundary for the coldest of the air this afternoon – and it stands out.
Low pressure around the South Island is the reason it’s warmer in the north and colder in the south – and on Thursday/overnight Thursday that colder air marches northwards to the lower North Island and the central North Island.
Over the weekend a low will deepen over the North Island and may turn stormy – it’s looking likely to bring a variety of possible severe weather including heavy snow, sub-zero wind chills, heavy rain, hurricane force winds, and dangerous seas. It’s a busy five days ahead – we’ll keep you posted!