A low pressure system to the east churns a very cold airflow over New Zealand today, tending westerly over the North Island and southwesterly for the South Island.

Northland, Auckland, Waikato & Bay Of Plenty
Showers, some may be heavy with hail / thunder. Conditions about the Bay Of Plenty especially in the east may not be as bad with some sun at times, still, showers will likely push through at times with a chance of small hail. Blustery west to southwesterly winds.
Highs: 13-15

Western North Island (including Central North Island)
Showers, some may be briefly heavy with small hail then a period of heavy showers / rain with hail moves through late afternoon / evening as northwesterly change southwest. Snow flurries likely about higher parts of the Central Plateau from afternoon. Conditions ease at night.
Highs: 5-13

Eastern North Island
Mostly sunny with breezy west to northwesterly winds, some rain for southern Wairarapa however. This rain spreads further north into Wairarapa in the afternoon as southwesterly winds strengthen with gales likely about the coast. Hawkes Bay and Gisborne sees cloud increase in the evening with winds tending more southwest.
Highs: 12-16

Wellington
Areas of rain, heavy at times with small hail especially afternoon as westerlies change strong to gale southerly.
High: 11

Marlborough & Nelson
Showers, clearing in the afternoon but staying mostly cloudy. Fresh southwester lies, strong to gale force winds about eastern coastal Marlborough.
Highs: 10-12

Canterbury
Morning heavy rain then easing afternoon to showers with a risk of small hail and snow flurries to 400m. Fresh cold southwesterlies, strong to gale about Banks Peninsula in the morning then easing.
Highs: 6-8

West Coast
Mostly sunny for South Westland, North Westland sees some rain or showers then clearing early afternoon. Winds cool from the south.
Highs: 10-13

Southland & Otago
Showers about Southland with small hail possible and snow flurries to 300m by midday. Otago has a dry morning with some sun possible, showers and a risk of small hail moves in late morning with snow flurries possible to 300m by evening. Fresh cold south to southwesterly winds with conditions easing at night for Southland and Central Otago.
Highs: 6-8

By Weather Analyst Aaron Wilkinson – WeatherWatch.co.nz