|WA Seasonal Rainfall Outlook: probabilities for Autumn 2007, issued 22nd February 2007|
Contrasting autumn rainfall odds in WA
The Western Australian outlook for total autumn (March to May) rainfall, shows that a drier than average autumn is more likely in the southwest, whereas above average falls are indicated further north in a zone stretching from the Pilbara to the interior.
The pattern of seasonal rainfall odds across WA is a result of higher than average temperatures in the Pacific Ocean (because of El Niño) and also in the Indian Ocean. More influence has come from the Pacific.
The chances of exceeding the median rainfall for the March to May period, are between 35 and 40% in parts of southwest WA south of Geraldton (see map). This means that BELOW median falls have about a 60 to 65% chance of occurring. So in years with ocean patterns like the current, about six autumns out of ten are drier than average and four out of ten are wetter in these regions with reduced odds.
In contrast, the chances of exceeding the median rainfall for autumn are between 60 and 70% in a wide band from northwest to central WA. So in years with ocean patterns like the current, about six or seven March to May periods out of ten are expected to be wetter than average across this region.
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 January Southern Oscillation Index (SOI) value was −7, a slight drop from the December reading of −3. The approximate SOI for the 30-days ending 19th February was −3.
The 2006/07 El Niño has ended. All the main ENSO indicators show that neutral conditions have returned to the Pacific Basin. For routine updates and comprehensive discussion on the latest data relating to El Niño, together with details on what the phenomenon is and how it has affected Australia in the past, 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 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 26th MARCH 2007