Bureau makes rain forecasts crystal clear

When you hear a weather forecast, can you tell the difference between isolated showers, scattered showers and patchy rain? What does the term "a chance of rain" really mean?

From this week, you won't have to know, thanks to the Bureau of Meteorology.

After decades in use, the BoM is revolutionising its rainfall forecasts to make them simpler and clearer for consumers.

Under the new system, adjectives such as patchy, scattered, widespread and isolated will be replaced with the straightforward terms slight, medium, high or very high to describe the chances of rainfall.

The chance of rain will also be expressed in percentage terms along with a forecast of how many millimetres of rain is expected.

The change is possible because of the BoM's new Meteye autographic information system, which divides the nation into six square kilometre grids and allows for highly localised meteorological observations and forecasting within each square.

BoM national public weather manager Vernon Carr said the old system has had its day.

"Basically, we're in a position (with Meteye) that we can give people a bit more detail about when it's going to rain and how much rain they're likely to get, whereas in the past it was just words.

"We did some research with people and we found that some of the terms we used weren't specific enough. Now we're changing to what we hope will be a more meaningful presentation.

"We're giving people a lot more background and detail now."

The new rain forecasts began in Tasmania and Western Australia today.

Victoria, NSW, the ACT and Queensland will begin in the new format tomorrow, followed by the Northern Territory on Wednesday and South Australia on Thursday.

RAIN FORECASTS BY THE PERCENTAGES:

* 0-10 pct - no mention of rain in forecast

* 20-30 pct - slight chance of rain

* 40-60 pct - medium chance of rain

* 70-80 pct - high change of rain

* 90-100 pct - very high chance of rain.