|WA Seasonal Rainfall Outlook: probabilities for Winter 2008, issued 27th May 2008|
Below average winter rainfall more likely in the southwest
The Western Australia outlook for total rainfall over winter shows an increased chance towards drier conditions in the southwest.
The pattern of seasonal rainfall odds across Australia is a result of higher than average temperatures in the Indian Ocean, and cooler than average waters in the central to western equatorial Pacific in association with the decaying La Niña pattern.
The chances of exceeding the median rainfall over winter are between 30 and 40%, or in other words there is a 60 to 70 % chance of below median rainfall in the southwest of WA. So for every ten years with ocean patterns like the current, about six or seven winter periods are expected to be drier than average, while about three or four are wetter. For the rest of the state, the chances of exceeding the winter median rainfall are 45 to 50%, meaning the odds of being wetter than normal are about the same as the odds of being drier. It should be noted, however, that this is a seasonally drier time of year over some northern parts of Australia.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During winter, history shows this influence in Western Australia to be generally weakly consistent, reaching moderate in patches (see background information).
The 2007/08 La Niña event in the Pacific Basin has decayed to neutral conditions: computer models indicate a continuation of neutral conditions through the forecast period. The 30-day value of the Southern Oscillation Index (SOI) was −3 as at 24th May. 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 information on this outlook is available from 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 26th June 2008