WA Seasonal Rainfall Outlook: probabilities for Winter 2004, issued 18th May 2004

Winter rainfall odds neutral over WA

The Bureau's winter rainfall outlook for Western Australia shows a pattern of neutral odds with no strong swings towards either wetter or drier conditions. This outlook pattern is a result of the combined effects of above average temperatures in both the Pacific and Indian Oceans.

For the June to August period, the chances of above median rainfall are mainly close to 50% right across the the state of WA (see map). So with climate patterns like the current, about five winters out of ten are expected to be drier than average over WA, with about five out of ten being wetter.

probability of exceeding median rainfall - click on the map for a larger version of the map

Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During winter, history shows this influence to be mainly weakly or very weakly consistent over the southern two-thirds of WA, and moderate in patches across the Kimberley where winter is a seasonally dry time of year (see background information).

Both the Indian and tropical Pacific Oceans remain mostly warmer than average, although the eastern Pacific has cooled. For more detail see the the El Niño Wrap-Up.

The Southern Oscillation Index (SOI) has been trending downwards over recent months with an April value of –15, following zero in March and +9 in February. The approximate SOI for the 30 days ending 15th May was +8.


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 information on this outlook is available from 9.00am to 5.00pm (WST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Perth Office: (08) 9263 2222.


Corresponding temperature outlook

April 2004 rainfall in historical perspective

February to April 2004 rainfall in historical perspective


Background Information