|WA Seasonal Rainfall Outlook: probabilities for Winter 2009, issued 26th May 2009|
No strong bias in winter rainfall odds for most of WA
The Western Australian outlook for total rainfall over winter (June to August), shows no strong bias in the odds favouring either wetter or drier conditions. In other words the chances of above normal falls are about the same as the chances of below normal.
The exceptions are in a few small patches in the southwest within which there are moderate shifts in the odds favouring a drier than average season.
The pattern of seasonal rainfall odds across WA is a result of recent warm conditions in the Indian Ocean and an increasing level of warmth in the Pacific.
For the June to August period, the chance of exceeding median rainfall is between 40 and 50% in most parts of the state (see map). This means that for every ten years with ocean patterns like the current, about four or five years are expected to be wetter than average during winter, while about five or six years are expected to be drier.
In small patches of southwest WA, the chances of a wetter than normal winter drop below 40% indicating an increased risk of dry conditions.
New: Under the WATL part of the Bureau's website, there is an expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm).
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During winter, history shows this influence generally to be weakly or very weakly consistent for a large part of Western Australia, reaching moderate only in patches (see background information).
Recent trends in Pacific climate patterns and the latest outputs from computer models indicate an increased risk of an El Niño developing during winter and spring. The SOI is approximately −11 for the 30 days ending 23 May. 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. More detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|More information on this outlook is available from 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 23rd June 2009