|WA Seasonal Rainfall Outlook: probabilities for January to March 2008, issued 17th December 2007|
Wetter March quarter favoured in southwest WA
The Western Australian outlook for total March quarter rainfall (January to March), shows a moderate to strong shift in the odds favouring above average totals in southwestern WA.
The pattern of seasonal rainfall odds across WA is a result of cooling 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 January to March are between 60 and 75% southwest of a line running approximately from Geraldton to Esperance (see map). However, it's a seasonally dry time of the year in this part of the State.
So for every ten years with ocean patterns like the current, about six or seven March quarters are expected to be wetter than average in southwest WA, while about three or four are drier.
Over the rest of the country, the chances of exceeding the three-month median rainfall are between 40 and 60%, apart from a small part of the Kimberley where the chances drop below 40%.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the March quarter, history shows the effect to be moderately consistent southwest of a line from Exmouth to Eucla, and in parts of far eastern WA. Elsewhere the effect is only weakly consistent (see background information).
A La Niña event is in progress across the Pacific Basin and computer models indicate it will persist at least until the early part of 2008. The 30-day value of the Southern Oscillation Index (SOI) was +8 as at 12th December. 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 9.00am to 5.00pm (WDST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th January 2008