National rainfall outlook

Issued 18 December 2013

Mixed seasonal outlook for Australia; drier for the east, wetter for the west

Text commentary of chance of increased rainfall

Summary

  • A drier than normal season is more likely for large parts of eastern Australia
  • A wetter than normal season is more likely for parts of western WA and southern Tasmania
  • The chances of a wetter or drier than normal season are roughly equal over the remainder of the country
  • Climate influences include a neutral tropical Pacific, and a warm Indian Ocean
  • Outlook accuracy is moderate over most of eastern Australia, the tropical north, western WA, and near the WA-NT border. Elsewhere, outlook accuracy is low. See outlook accuracy tab for more information.
Probability of exceeding median rainfall, large image

Details

The chances of exceeding the median rainfall during the January to March period are 30 to 40% over most of Queensland, parts of the eastern NT, most of NSW and northeast Victoria. In other words, the chances of below average rainfall are 60 to 70% over these areas. So, for every ten summer outlooks with similar odds to these, about three or four of them would result in above-average rainfall over these areas, while about six or seven would be below average.

Conversely, the chance of exceeding the median rainfall is greater than 60% over parts of western WA and most of Tasmania.

The chance of receiving a wetter or drier than normal January to March period is roughly equal (i.e., close to 50%) over the remainder of the country.

Climate influences

The El Niño-Southern Oscillation (ENSO) remains neutral, with the majority of atmospheric and oceanic indicators close to their long-term average. Dynamical models surveyed by the Bureau suggest ENSO-neutral conditions are likely to persist at least for the austral summer and early autumn. This means there is no strong shift in the odds from the tropical Pacific in this outlook.

Although the Indian Ocean Dipole has limited impact upon Australia during the months from December to April, the broad area of warmer than average sea surface temperatures across the central Indian Ocean has been shown to influence the climate over large parts of Australia at this time of year.

Lower surface pressures are likely to bring cooler and potentially wetter conditions to parts of southern Australia (such as Tasmania and parts of southwest WA) early in the outlook period. For northern regions, tropical Australian sea surface temperatures are currently average to slightly cooler than average, and are expected to remain that way over the forecast period. Weak to moderate tropical activity (cloud and rainfall associated with the Madden-Julian Oscillation) is expected in the first month.

How accurate is the outlook?

Outlook accuracy for the January to March period is:

  • Moderate over much of eastern Australia, the tropical north, western WA and an area near the WA-NT border
  • Weak over eastern WA, western parts of the NT and SA, and southeast SA
  • Very weak over northeast SA, northwest NSW, southwest Queensland and parts of the southeast NT