|National Seasonal Rainfall Outlook: probabilities for Autumn 2007, issued 22nd February 2007|
Mostly neutral autumn rainfall odds, except in WA
The national outlook for total autumn (March to May) rainfall, generally shows no strong swings in the odds towards wetter or drier conditions. In WA however, 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 Australia 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. However, over most of the country the chances of exceeding the seasonal median are between 40 and 60%.
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 the north and west of the country. Elsewhere the effect is only weakly or very weakly consistent (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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Blair Trewin on (03) 9669 4623, Lyn Bettio on (03) 9669 4165.|
Regional commentary is available from the Climate Services Centres in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 26th MARCH 2007