The old adage that you can never trust the weather forecast may have some truth to it in New Zealand.

A Ministry of Business, Innovation and Employment report, released this afternoon, has found that the Government has a monopoly on New Zealand weather data, which is stifling innovation and research.

The report - Weather Permitting: Review of open access to weather data in New Zealand - was finished last April but only published today. It found that access to weather data was costly and restrictive when compared with the USA, Norway, Australia, the UK and France.

"The New Zealand model is at the most commercial and restrictive end of cost and limitations on data use ... Some people believed that MetService and Niwa used their monopoly on weather data to stifle competition in the market for value-added services."

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Costly access to data was in part due to the funding models for MetService and Niwa, which were more reliant on Government subsidies than other countries.

"The key is balancing the monopoly industry (MetService and Niwa) that produces weather observational data, and the competitive industry that uses data as a resource," the report said.

Weatherwatch.co.nz head forecaster Philip Duncan told the Herald that opening up access to the data would increase competition and lift forecasting accuracy.

"The average New Zealander says the forecasts in this country are terrible. They don't believe the weather warnings. That's very concerning.

"We don't even publish MetService weather warnings because they are so inaccurate and have a history of being dramatic. Open data does actually improve accuracy.

"The Government needs to decide what is more important - open data that taxpayers have already funded, or continuing to allow MetService and Niwa to have exclusive commercial access to data. I shouldn't have to pay $600 a day to drive on an NZTA highway, or $600 a day to share with you tax-funded data."

The report was completed in April last year but was only released today, after Duncan vented over Twitter.

"Not one single person at @MBIEgovtnz or @Megan_Woods office can now tell me who is even in charge of the #OpenWeatherReview. No one at all. No accountability. No transparency. No professionalism. No replies," he tweeted yesterday.

Duncan accused the previous National-led Government of burying the report in an election year.

"We knew the report was going to say that data should be freed up, but the Government will have to work out how Niwa and MetService make a profit. It's a tough job. National didn't want to touch it."

A spokesman for Science and Innovation Minister Megan Woods said the minister has requested officials to take a close look at the sector, "especially if the commercial model is causing issues".​