Forecasting gains more authority

He said accuracy had increased "through gradual gains and a series of leaps".

"In the past 30 years in particular, models to simulate the entire atmosphere are steadily getting more skilful," Dr Tupper said.

"A five-day forecast is generally considered to be as reliable as a two-day forecast was 30 years ago."

He said there were several factors that had contributed to this improvement, including investments in supercomputers to run weather models, and access to satellites.

Dr Tupper said seasonal forecasts could still be difficult to predict with accuracy.

"Beyond a couple of weeks, if predicting what will happen and when, we start to run into problems," he said.

But he said there had been some improvement in this area.

"We used to use statistics, such as 'the summer looks like some of the summer of 1983, with oceans patterns similar to another year', and we'd put it together for a forecast," he said.

This methodology still has a role, but models and simulations also contribute.

"We're able to calculate what happens next based on what is happening now, instead of loosely looking at the past," Dr Tupper said.

He said a number of models available, internationally and locally, were a way to check the likelihood of an event.

"If they're all telling us the same thing, we can have a fair amount of confidence," Dr Tupper said.

"This leads us to say 'there is a 90 per cent chance this will happen'.

"With probability we try to help people understand the risk."

He said this approach was not perfect as evidenced by the BoM making the unusual decision to release a fresh season update for coming months.

"It is an unusual thing for us but conditions changed so markedly," Dr Tupper said.

The past month has seen another big jump in accuracy, with Australia having access to new Japanese satellite Himawari-8, which can be seen online at the BoM site with real-time images.

"We have observations every 10 minutes, in full colour, with a number of different spectral bands, so we can use it a lot more," Dr Tupper said.

He said it was especially important in Australia where a large landmass and lower comparable population could make it tricky to get land observations.