Forecasts

WEATHER FORECAST

National Seasonal Rainfall Outlook: probabilities for May to July 2010, issued 22nd April 2010

Increased rainfall odds for eastern Australia

The national outlook for total rainfall over the late autumn to mid-winter period (May to July), shows a moderate to strong shift in the odds favouring a wetter than normal season over parts of north and eastern NSW and southern parts of Queensland.

The pattern of seasonal rainfall odds across Australia has been produced using recent Pacific and Indian Ocean temperature patterns. The Indian Ocean is dominant in this outlook with reinforcement from the Pacific.

The chances of exceeding the median rainfall for May to July are above 60% over the southern third of Queensland and across northern and eastern NSW (see map). Within this region, the chances of a wetter than normal three months exceed 75% in an area straddling the NSW/Qld border centred near Goondiwindi.

This means that for every ten years with ocean patterns like the current, about six to eight May to July periods are expected to be wetter than average over this broad region of eastern Australia, while about two to four periods are drier.

Contrasting this, the chances are between 35 and 40% for above average May to July falls in several small regions in southern Australia, mainly in WA and Victoria. This means that above normal falls would be expected to occur in around three or four years for every ten that ocean patterns are similar to the present.

Across the rest (and most) of the country, the chances of exceeding the median May to July rainfall are between 40 and 60%, meaning that above average falls are about as equally likely as below average falls.

An expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm), is available on the "Water and the Land" (WATL) part of the Bureau's website.

Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the late autumn to mid-winter period, history shows this effect to be moderately consistent in a band from the central Northern Territory across most of the southern two-thirds of Queensland, as well as the northeastern half of NSW. Moderate consistency is also evident in much of Tasmania, parts of southern Victoria, and patches through the interior of Western Australia. Elsewhere the effect is only weakly or very weakly consistent. (see background information).

The El Niño event across the Pacific Basin has continued to break down during the past month. Most leading climate models indicate further cooling and a return to a neutral (near-average Pacific temperatures) pattern by the southern winter. The SOI is approximately +11 for the 30 days ending 19 April. For routine updates and comprehensive discussion on any developments regarding El Niño or La Niña, 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.