|National Seasonal Rainfall Outlook: probabilities for Summer 2006/2007, issued 23rd November 2006|
Decreased summer rainfall in parts of north Qld
The latest seasonal rainfall outlook issued by the Bureau of Meteorology shows a moderate shift in the odds towards below-normal summer (December to February) rainfall for parts of north Queensland. However, across most of the country the chances of accumulating at least average (median) rain during the coming three months are close to 50%.
The pattern of seasonal rainfall odds across Australia is a result of competing effects from higher than average temperatures in both the Pacific and Indian Oceans. The warm Pacific (because of El Niño) biases the climate towards drier than average in eastern Queensland and NSW as well as in northwest WA, while the warm Indian Ocean promotes wetter than average conditions in these same areas. Hence, the two signals largely cancel each other.
The chances of exceeding the median rainfall for the December to February period, are between 35 and 40% over an area of north Queensland centred roughly on Charters Towers. 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 summers out of ten are expected to be drier than average over this region in north Queensland, with about four out of ten being wetter.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During summer, history shows this effect to be moderately consistent across much of WA and scattered areas in eastern Australia, but the effect is generally weakly or very weakly consistent through the centre of the country (see background information).
The Southern Oscillation Index (SOI), negative for the sixth straight month as a result of the El Niño, fell from −5 in September to −15 in October. The approximate SOI for the 30 days ending 20th November was −7.
The current Pacific El Niño pattern, of which the low SOI is but one indicator, is expected to persist for most of the summer. 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.
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|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Lyn Bettio on (03) 9669 4165, David Jones on (03) 9669 4085.|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 20th DECEMBER 2006