|National Seasonal Rainfall Outlook: probabilities for Spring 2008, issued 26th August 2008|
Mixed spring rainfall odds
Although the national outlook for total spring (September to November) rainfall is neutral for most of the country, there are mixed odds in parts of southern Australia. A moderate to strong shift in the odds favouring above average rainfall in southwest WA contrasts with the situation through parts of central and southern SA where a drier spring is the more likely outcome.
The pattern of seasonal rainfall odds across Australia is mainly a result of continued warmth in the central and southeastern Indian Ocean, especially off the west coast of WA.
The chances of exceeding the median rainfall for spring are between 60 and 75% over southwest WA (see map). So for every ten years with ocean patterns like the current, about six or seven springs are expected to be wetter than average in southwest WA, while about three or four are drier.
In contrast, the chances of exceeding the spring median are between 35 and 40% across a region of central to southern SA, roughly centred on Port Augusta. This means below average falls have a 60 to 65% chance of occurring. However, over most of the nation the chances of a wetter than normal spring are between 40 and 60%, meaning that above average falls are about as equally likely as below average totals.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent across most of the eastern mainland states and the NT, as well as northern Tasmania, southwest and far northwest WA, and parts of SA (see background information).
The approximate 30-day value of the Southern Oscillation Index (SOI) was +3 as at 23 August, while a mixed pattern of warmer and cooler than normal temperatures persists along the equatorial Pacific Ocean. Both these observations indicate a neutral climate pattern across the Pacific, which computer models indicate is likely to continue for the next few seasons. For routine updates and comprehensive discussion on any developments please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Lyn Bettio on (03) 9669 4165, Blair Trewin on (03) 9669 4623, Clinton Rakich on (03) 9669 4671.|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 25th September 2008