WA Seasonal Rainfall Outlook: probabilities for February to April 2004, issued 15th January 2004

Neutral seasonal rainfall odds

The Bureau's seasonal rainfall outlook for late summer to mid-autumn shows no strong swings in the odds towards wetter or drier conditions in Western Australia. The chances of above average seasonal falls are generally close to a neutral 50%. This outlook is due to the fact that Pacific and Indian Ocean temperatures have a varying influence on Australian rainfall during summer and autumn.

For the February to April period in WA, the chances of above median rainfall are between 40 and 55% (see map). So with climate patterns like the current, about 5 seasons out of 10 are expected to be wetter than average over the State, with about 5 out of 10 being drier.

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 the February to April period, history shows this influence to be moderately consistent through most of WA (see background information).

The tropical Pacific Ocean cooled during December, but there was little change in tropical Indian Ocean temperatures. For more detail see the El Niño Wrap-Up. The temperature patterns in the Indian and Pacific Oceans are not extreme enough to produce large swings in the outlook probabilities.

December's value of the Southern Oscillation Index (SOI) was +10, a strong rise from the –3 recorded in November. The rise in the SOI was in part caused by below average air pressure over northern Australia associated with a strong onset to the monsoon. The approximate SOI for the 30 days ending 12th January was +2.


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

December 2003 rainfall in historical perspective

October to December 2003 rainfall in historical perspective


Background Information