What's behind weather forecasts?

A big storm is coming, and graphs are everywhere. Inside the MetService situation room in Kelburn, all eyes are on the graphs, not on the gloomy but expansive views across Wellington.

Every morning, about 20 of our top weather forecasters sit around "nodding". The term is from a time when a wise old lead forecaster would pontificate on his weather predictions at the MetService's base above Kelburn, while his juniors nodded in deference.

These days, weather balloons are no longer launched from the roof. Junior forecasters are now welcome to weigh in.

The biggest difference, though, is technology. It is everywhere. Four computers can sit on a single desk, showing predictions of the coming weather.

Even so, they reckon technology gives them only 60 per cent of the story. The rest is real people's interpretations, informed by masses of computer-generated graphs.

At 9.50am, a bell rings. As yet more graphs churn out of a noisy printer, the forecasters gather around. Lead forecaster Matt Ford has the floor, flicking through computer models that have come from around the world.

To a novice it is a tangle of isobars, troughs and lows. Each forecaster pays intense attention. To them, it means a lot.

Forecaster Dan Corbett, the face of the MetService, watches intensely, a finger pressed to his lips. Soon his phone will be ringing hot as media throughout the country look for the latest news, as decided by yesterday's meeting, on what to expect from a large intense low pressure system rolling in from the south.

Mr Corbett is tasked with making it digestible to the public. He is famed for his colourful descriptions, such as the coming "rip- snorting southerly" with gusts of up to 130kmh in exposed places. "It's got fangs as teeth and it's ugly."

Down the stairwell, public weather services manager Ramon Oosterkamp points out a series of cartoons, many making fun of the MetService when it gets it wrong. In the foyer, he shares the proof that most of the time MetService gets it right. Of severe weather warnings issued, 92 per cent turn out to be right. In the mid-1980s, that figure was about 80 per cent.

The Dominion Post