National Seasonal Temperature Outlook: probabilities for Autumn 2012, issued 22nd February 2012
The autumn 2012 temperature outlook shows the following:
This outlook is mostly due to warmer than normal waters over the Indian Ocean; cooler Pacific waters associated with La Niña have had a lesser impact.
The chances that the average minimum temperature for autumn will exceed the long-term median minimum temperature are above 60% across the eastern mainland of Australia, the southern half of WA and the Top End of the NT. Probabilities exceed 80% across southwest WA and northeast Queensland (see map above).
History shows the oceans' effect on minimum temperatures during the autumn period to be moderately consistent over most of Australia, except for the southern NT, SA and NSW, where the skill is only weakly to very weakly consistent. Users should exercise caution when using this outlook in these areas of low skill.
The chances that the average autumn maximum temperature will exceed the long-term median maximum temperature are 60 to 70% over western WA (see map above). This means that for every ten years with ocean patterns like the ones currently observed, autumn would be expected to be warmer than average in about six or seven years over this area, with the other three or four years being cooler. In contrast, there is a 25 to 40% chance of warmer than normal autumn days over southern Queensland, the northern half of NSW and northeast SA. In other words, there is a 60 to 75% chance of a cooler season over this region.
However, we advise caution using this outlook because of the low confidence across the southern half of the country at this time of year.
Elsewhere, the chances of a warmer or cooler autumn are roughly equal.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian temperatures. During the autumn period, history shows this effect on maximum temperatures to be moderately consistent over the northern half of Australia, and parts of Victoria and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent (see background information).
Click on the maps above for larger versions of the maps. Use the reload/refresh button to ensure the latest forecast maps are displayed.
The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Andrew Watkins on (03) 9669 4360, Grant Beard on (03) 9669 4607, Catherine Ganter on (03) 9669 4679.
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
|Queensland -||(07) 3239 8660|
|New South Wales -||(02) 9296 1555|
|Victoria -||(03) 9669 4949|
|Tasmania -||(03) 6221 2043|
|South Australia -||(08) 8366 2664|
|Western Australia -||(08) 9263 2222|
|The Northern Territory -||(08) 8920 3813|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 21st March 2012
The Bureau's seasonal outlooks are general statements about the probability or risk of wetter or drier than average weather over a three-month period. The outlooks are based on the statistics of chance (the odds) taken from Australian rainfall/temperatures and sea surface temperature records for the tropical Pacific and Indian Oceans. They are not, however, categorical predictions about future rainfall, and they are not about rainfall within individual months of the three-month outlook period. The temperature outlooks are for the average maximum and minimum temperatures for the entire three-month outlook period. Information about whether individual days or weeks may be unusually hot or cold, is unavailable.
This outlook is a summary. More detail is available from the contact people.
Probability outlooks should not be used as if they were categorical forecasts. These outlooks should be used as a tool in risk management and decision making. The benefits accrue from long-term use, say over 10 years. At any given time, the probabilities may seem inaccurate, but taken over several years, the advantages of taking account of the risks should outweigh the disadvantages. For more information on the use of probabilities, farmers could contact their local departments of agriculture or primary industry.
Model Consistency and Outlook Confidence: Strong consistency means that tests of the model on historical data show a high correlation between the most likely outlook category (above/below median) and the verifying observation (above/below median). In this situation relatively high confidence can be placed in the outlook probabilities. Low consistency means the historical relationship, and therefore outlook confidence, is weak. In the places and seasons where the outlooks are most skilful, the category of the eventual outcome (above or below median) is consistent with the category favoured in the outlook about 75% of the time. In the least skilful areas, the outlooks perform no better than random chance or guessing. The rainfall outlooks perform best in eastern and northern Australia between July and January, but are less useful in autumn and in the west of the continent. The skill at predicting seasonal maximum temperature peaks in early winter and drops off marginally during the second half of the year. The lowest point in skill occurs in early autumn. The skill at predicting seasonal minimum temperature peaks in late autumn and again in mid-spring. There are also two distinct periods when the skill is lowest - namely late summer and mid-winter. However, it must always be remembered that the outlooks are statements of chance or risk. For example, if you were told there was a 50:50 chance of a horse winning a race but it ran second, the original assessment of a 50:50 chance could still have been correct.
The Southern Oscillation Index (SOI) is calculated using the barometric pressure difference between Tahiti and Darwin. The SOI is one indicator of the stage of El Niño or La Niña events in the tropical Pacific Ocean. It is best considered in conjunction with sea-surface temperatures, which form the basis of the outlooks. A moderate to strongly negative SOI (persistently below −10) is usually characteristic of El Niño, which is often associated with below average rainfall over eastern Australia, and a weaker than normal monsoon in the north. A moderate to strongly positive SOI (persistently above +10) is usually characteristic of La Niña, which is often associated with above average rainfall over parts of tropical and eastern Australia, and an earlier than normal start to the northern monsoon season. The Australian impacts of past El Niño events since 1900 are summarized on the Bureau's web site (El Niño - Detailed Australian Analysis), and past La Niña events (La Niña - Detailed Australian Analysis)
© Australian Government, Bureau of Meteorology