|National Seasonal Rainfall Outlook: probabilities for Autumn 2008, issued 26th February 2008|
Mixed autumn rainfall outlook
The national outlook for autumn rainfall (March to May), shows a mixed pattern of odds: a wetter than normal season is favoured in northern Queensland and in parts of NSW and SA, while below-normal falls are more likely in parts of Victoria and Tasmania.
The pattern of seasonal rainfall odds across Australia is a result of cooler than average waters across the equatorial Pacific in association with La Niña, and continuing higher than average temperatures in the central to southeastern Indian Ocean.
The chances of exceeding the median rainfall over March to May are between 60 and 70% over most of north Queensland, and between 60 and 65% in a band extending from central SA to the far west of NSW (see map). So for every ten years with ocean patterns like the current, about six or seven autumns are expected to be wetter than average in these parts of the country, while about three or four are drier.
In contrast, areas in northern and central Tasmania together with parts of Victoria's coastal fringe have a 35 to 40% chance of exceeding the autumn median. This means that a drier than normal autumn is a 60 to 65% chance in these regions.
Over the rest of the country, the chances of exceeding the three-month median rainfall are between 40 and 60%. So the chances of being wetter than normal are about the same as the chances of 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 the north and west of the country. Elsewhere the effect is only weakly or very weakly consistent (see background information). So swings in the odds to below or above average rainfall outside of Queensland need to be viewed with caution as the confidence level is low.
A La Niña event is in progress across the Pacific Basin and computer models indicate it is likely to persist until the end of autumn. The 30-day value of the Southern Oscillation Index (SOI) was +20 as at 23rd February. For routine updates and comprehensive discussion on any developments 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: Lyn Bettio on (03) 9669 4165, Blair Trewin on (03) 9669 4623 Brad Murphy on (03) 9669 4409.|
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 28th March 2008