|National Seasonal Rainfall Outlook: probabilities for February to April 2009, issued 22nd January 2009|
Mixed rainfall odds for late summer to mid-autumn
The national outlook for total late summer to mid-autumn (February to April) rainfall, shows mixed odds for exceeding the seasonal median. There is a moderate to strong shift in the odds favouring higher than normal rainfall over much of WA as well as for an area covering southern SA. Conversely, there is a moderate shift in the odds favouring lower than normal rainfall over parts of central and northern Queensland.
The pattern of seasonal rainfall odds across Australia is mainly a result of a cooling trend in the Indian Ocean, the Pacific Ocean had little contribution to this forecast.
The chance of exceeding median rainfall over Australia during February to April is between 60 and 75% over western WA and between 60 and 65% over northern WA into the NT and in southern SA. This means that for every ten years with ocean patterns like the current, about six or seven years are expected to be wetter than average in these regions, while about three or four years are expected to be drier.
In contrast, the odds of exceeding median rainfall over much of central and northern Queensland are between 20 and 40%, which means that these areas have a 60 to 80% chance of being drier than normal.
Across the rest of the country, the chance of exceeding the median rainfall during February to April is between 40 and 60%, meaning that above average falls are about as equally likely as below average falls in these regions.
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 parts 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).
The central and eastern equatorial Pacific Ocean cooled further during December. This brings the Pacific Ocean into line with atmospheric indicators, a number of which have been approaching La Niña levels since October 2008. However, most current model outlooks, and a build-up of warmer sub-surface water in the western equatorial Pacific, suggest that the cooler conditions in the Pacific may not persist beyond summer 2009. The most likely scenario is for the central and eastern Pacific to warm over the coming months and hence remain neutral. The SOI remains positive at approximately +13 for the 30 days ending 19 January. 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. More detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Lynette Bettio on (03) 9669 4165, Brad Murphy on (03) 9669 4409, 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 February 2009