Rain has fallen on five of the first 10 days of 2012, and totals 50mm already at the Westpac Agricultural Research Station near Hawera.

Since December 29, 188mm of rain has fallen at the research station - on eight days.

Milk production dropped 1.5 litres per cow per day after Sunday's storm, Hawera farm adviser Debbie McCallum said. "We need a good dose of sunshine and production will stabilise."

Continuing wet weather was frustrating for farmers. "We've had almost too much rain and too many wet cloudy days," she said.

Some farmers were having problems getting hay in - although on the other hand they would be well set up for when the sun did shine.

McCallum said dairy farmers could expect good production this month because soil moisture levels would remain high.

"Little supplement will need to be fed. Enjoy the growing conditions.

"Farmers can cruise through on all grass."

The season had been a mixed one, with snow in August and a dry spell in late November.

That month was cold, dull and overcast and silage crops were late, but December was good.

McCallum said its rainfall of 260mm was the highest recorded at the Westpac Agricultural Research Station since 1977 and historical data indicated it was possibly the highest ever.

The rainfall for 2011 was 1578mm, well above the 110mm average and more than twice the 1983 low of 766mm. In January 180mm fell and 260mm was recorded in December, both months when rainfall is normally low