Yes, it was a shocker.

Snow, frost, hail and a tornado marked the first month of summer, with the coldest temperatures recorded in December since 1945.

National Institute of Water and Atmospheric Research figures for last month show it was the fifth coldest since records were established in 1853. The national average temperature was just 13.4C - 2.2C below normal and more like spring than summer.

The record-breaking low temperatures not only kept the summer clothes in the cupboard but slowed the growth and ripening of berries, stone fruit and crops.

Southerlies produced dramatic amounts of rain, with more than double normal rainfall in eastern regions from Hawkes Bay to Southland. Rainfall was also well above average in Auckland, Coromandel, Waikato, Ruapehu and Wanganui.

Despite that, less than three-quarters of average rainfall was recorded in sheltered parts of Fiordland and south Westland.

And if you thought there was a dire shortage of sun, there was.

Auckland recorded only 174 hours of sunshine - 83 per cent of the normal figure and the third lowest since records began in 1963.

Of the four main centres, Wellington was the sunniest and Christchurch the driest.

Niwa principal climate scientist Dr Jim Salinger said the above-average number of lows centred south of the Chatham Islands produced the strongest south-to-southwest airflow over New Zealand on record.

But don't despair. Things are going to improve, apparently.

Dr Salinger said northern New Zealand could expect more westerly winds, more settled weather and warmer temperatures late this month and next. The large number of lows was unlikely to repeat itself in January.

"Last holiday period, Christmas and New Year were perfect. This year it has been the opposite," Dr Salinger said. "Each season plays itself out differently than the previous year. My expectation is that January will improve."

Cold and wet

Coldest December since 1945.

Lowest temperature of minus 3.7C recorded in Southland on the 20th.

Frost in inland areas of the North Island and the South Island.

Gale force southerlies brought hail to Auckland, Port Waikato, Hawkes Bay, Tasman and Canterbury.

Snow in the South Island to 600m and light snow on the Desert Road in the Central North Island.

Eastern regions from Hawkes Bay to Southland had more than double their normal rainfall.