WA Seasonal Rainfall Outlook: probabilities for Spring 2004, issued 17th August 2004

Neutral outlook for Spring rainfall in WA

Although below average falls are favoured in parts of southeastern Australia, there are a no strong shifts in the odds towards either below or above average spring rainfall in Western Australia, the Bureau of Meteorology announced today.

So across WA, the chances of above median rainfall for spring are mainly between 50 and 60%. So in years with ocean patterns like the current, about five spring periods out of ten are expected to be drier than average, with about five out of ten being wetter.

However, through northwest and parts of northern Western Australia, spring is a seasonally dry time of year and heavy rain during this period is uncommon.

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

The current pattern of outlook probabilities is due to recent temperature patterns in both the Pacific and Indian Oceans.

Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During spring, history shows this influence to be moderately consistent in only the southwest and far northwest of the State (see background information). Elsewhere the influence is largely very weakly consistent.

The Southern Oscillation Index (SOI) has remained significantly negative for the second successive month, with a July value of –7 following the June reading of –14. The approximate SOI for the 30 days ending 14th August was –12. Consistent with the negative SOI, the central Pacific has been warming over the past few months. However, given historical precedent and the current model guidance, the triggering of an El Niño event during the second half of 2004 is less likely than the persistence of neutral conditions. For more detail see the El Niño 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 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.
 

THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 16th SEPTEMBER 2004.

Corresponding temperature outlook

July 2004 rainfall in historical perspective

May to July 2004 rainfall in historical perspective

 

Background Information