Mr Anderson leads Agriculture Victoria's seasonal risk team, responsible for The Break updates, soil moisture monitoring and the Climatedogs series.

He's the first to say that forecasts are not perfect and farmers need to know which data they can trust.

"Nobody can reliably predict the future but we're not flying blind," Mr Anderson said.

"The analogy is that farmers will have a model in their head for a particular paddock; they'll know what sort of wheat yield to expect off it in an average year based on a mental model based on its history.

"But then it's important that farmers know there are potential curve balls like armyworm, droughts or frosts that have a big impact on whether that will happen and a weather forecast is no different."

Often, knowing the uncertainty was just as important as knowing the total.

"Find a forecast you can understand, know where it's from - and there are plenty that are not from the Bureau of Meteorology - and see if it's got a bit of a range because, the bigger the range, the lower the confidence."

The seasonal, three-month, forecasts were expressed in probabilities that often brought farmers unstuck.

"If there's a 50 per cent chance of mean rainfall, that doesn't mean you're getting an average year, it just means there's an equal chance of it being wetter or drier than usual and all options are possible," Mr Anderson said.

"They're more reliable in winter and spring for south-east Australia when there are a lot of events we can watch to see trends but, usually in autumn, they're more variable and totals depend on just a few weather events."

And the reliability of climate change models?

"Climate projections use all the same physics that go into weather and seasonal models but they also consider the changing energy levels in the atmosphere, which is where the greenhouse gases come in," he said.

He said that, while there were many complexities yet to be understood, the fundamentals were very clear.

In the 1850s, scientists noted that not all the heat from the sun was not lost overnight and ran experiments to see how much energy different gases trapped.

"They found that the more greenhouse gases there were, the more heat was trapped."

Graeme Anderson will present a webinar, Weather Forecasts, Seasonal Outlooks and Climate Change Projections - What they can and can't do, on March 11.