|National Seasonal Rainfall Outlook: probabilities for February to April 2007, issued 23rd January 2007|
Mixed rainfall odds for late summer to mid-autumn
The national outlook for total February to April rainfall, shows a mixed pattern of odds, with below average totals indicated over northern Queensland contrasting with an increased chance of above-normal falls in a band from northwest WA to western Victoria.
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 February to April period, are below 40% in the northern half of Queensland, dropping to below 25% in the region near Hughenden. This means that BELOW median falls have about a 60 to 75% chance of occurring. So in years with ocean patterns like the current, about six or seven February to April periods out of ten are expected to be drier than average in this part of the country, with about three or four out of ten being wetter.
In contrast, the chances of exceeding the median rainfall for the coming three months are between 60 and 75% over northwest and central WA, and between 60 and 65% in southern SA, western Victoria and a small part of northern Tasmania. So in years with ocean patterns like the current, about six or seven February to April periods out of ten are wetter than average and three or four out of ten are drier in these regions with elevated odds.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the February to April period, history shows the effect to be moderately consistent through the northern halves of both Queensland and the NT, most of WA, the far west of SA and southeast NSW. Elsewhere the effect is only weakly or very weakly consistent (see background information), so the increased odds in SA and Victoria should be applied with caution.
December was the second successive month when the Southern Oscillation Index (SOI) was only slightly negative, with a monthly value of −3 following the −1 in November. A link to 30-day SOI values is available in the ENSO Wrap-Up (see next paragraph).
The neutral SOI is one of a few indicators which show that the current Pacific El Niño pattern is beginning to weaken. 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: Blair Trewin on (03) 9669 4623, Andrew Watkins on (03) 9669 4360.|
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 22nd FEBRUARY 2007