MetService says thunderstorms and possibly damaging winds will likely affect much of the northern North Island from this morning.
An unstable flow of cold air is pushing onto the country from the southwest, bringing heavy rain and wind gusts in places of up to 110km/h.
MetService's latest thunderstorm outlook says Auckland, Waikato, Taranaki, Northland and Coromandel all have a moderate risk of squally thunderstorms this morning, and into the afternoon.
Those storms could continue in Auckland and Northland until this evening.
There's a lower risk of storms reaching further inland to southern Taranaki and the central plateau.
The Bay of Plenty and Tauranga can also expect storms this afternoon.
MetService says the inclement weather could bring hail and even some small tornadoes near the coast.
A heavy snow watch is also in place for much of the Southland area, with snow expected right down to 300 metres above sea level, and heavier above 400 metres.
Snow is also likely on the central plateau around the Desert Road, Taihape, Raetihi and Ohakune.
ROAD SNOWFALL WARNINGS
A road snowfall warning is in place for State Highway 5 in Hawke's Bay (the Napier-Taupo road), where small amounts of snow could settle on the road at heights above 800m after 4pm today.
A snowfall warning has also been issued for Desert Road, with light snow predicted this morning until 3pm, getting heavier from there until about 9pm - up to 10cm could fall.
Lewis Pass could see up to 3cm of snow until 11am this morning, while Arthurs Pass and Porters Pass could see a lesser amount early this morning.
The road between Dunedin and Waitati could also see some snow between midday and midnight, but only about 1cm near the summit.
Lindis Pass could see some snow, but MetService says not much of it will settle on the road.
The Crown Range Road may see some snow this morning, with up to 2cm settling.
Milford Road could see snow this morning down to 400 metres, but it will likely ease from this afternoon.