|WA Seasonal Rainfall Outlook: probabilities for Autumn 2006, issued 21st February 2006|
50:50 chances for a wetter than average autumn
The chances of accumulating at least median rain during autumn (Mar-May) are close to 50% across the entire country, the Bureau of Meteorology announced today. The outlooks are based on relationships between Pacific and Indian Ocean temperatures and Australian rainfall. Recent ocean temperatures have not been sufficiently warmer or cooler than average to produce a strong bias in rainfall outlook odds.
For the March to May period, the chances of above median rainfall are between 50 and 60% across much of central and northwest WA, dropping to a little below 50% in the far southwest and far northeast (see map).
So in years with ocean patterns like the current, about five or six autumns out of ten are expected to be wetter than the median over the State, with about four or five out of ten being drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During autumn, history shows this effect to be moderately consistent across much of WA, particularly in the southern half of the State (see background information).
The Southern Oscillation Index (SOI) rose from +1 in December to +13 in January. The approximate SOI for the 30 days ending 18th February was +4. The recent positive SOI values are consistent with developments towards La Niña conditions in the Pacific Ocean. More information is available in the 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 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 23rd MARCH 2006