Northern Aust Seasonal Temperature Outlook: probabilities for April to June 2010, issued 23rd March 2010
The outlook for mean maximum and minimum temperatures during April to June shows a moderate to strong chance of warmer than normal conditions over much of northern Australia.
The chance that the average April-June maximum temperature will exceed the long-term median maximum temperature, is between 60 and 85% across the northern halves of both Queensland and the NT (see map). This means that for every ten years with SST patterns like the current, about six to eight April to June periods are expected to be warmer than average over these areas, while around two to four periods are cooler.
In contrast, the chance of a warmer than normal three months is between 35 and 40% over southeast Queensland, which means there are about six chances out of ten that the April-June period will be cooler than usual. This is consistent with the outlook favouring above normal rainfall over the same region. In remaining parts of northern Australia, a warmer or cooler than average three months are both about as equally likely.
The pattern of seasonal temperature odds across Australia is due to recent higher than average sea surface temperatures (SST) in both the Pacific (El Niño) and Indian Oceans.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian temperatures. During the June quarter, history shows the effect on maximum temperatures to be moderately consistent over most parts of the NT and Queensland, with the exception of some southern areas in both (see background information).
The average minimum temperature for April to June is favoured to be above the long-term median minimum temperature across all of northern Australia (see map). The chance of increased overnight warmth is between 65% and 85%, with the highest probabilities being located over Queensland's eastern half.
History shows the oceans' effect on minimum temperatures in the April to June period to be moderately consistent over large parts of northern Australia, except for the southwest corner of the Northern Territory where it is only weakly or very weakly consistent.
Click on the maps above for larger versions of the maps. Use the reload/refresh button to ensure the latest forecast maps are displayed.
More information on this outlook is available by contacting the Bureau's Climate Services sections in Queensland and the Northern Territory at the following numbers:
|Brisbane -||(07) 3239 8660|
|Darwin -||(08) 8920 3813|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 22nd April 2010
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 or from SILO (Seasonal Climate Outlook Products).
Probability outlooks should not be used as if they were categorical forecasts. More on probabilities is contained in the booklet The Seasonal Climate Outlook - What it is and how to use it, available from the National Climate Centre. 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 25 El Niño events since 1900 are summarized on the Bureau's web site (El Niño - Detailed Australian Analysis).
© Australian Government, Bureau of Meteorology