Cool nights favoured for the dry season in the Territory

Northern Aust Seasonal Temperature Outlook: probabilities for Winter 2011, issued 24th May 2011

Cool nights favoured for the dry season in the Territory

The north Australian outlook for maximum and minimum temperatures averaged over the dry season months of June to August favours cooler night-time temperatures across the Northern Territory.

This outlook is a result of cool conditions in the central tropical Pacific Ocean, as well as warm conditions in the Indian Ocean.

The chance that the average dry season (June to August) maximum temperature will exceed the long-term median maximum temperature ranges from 40% in southeast Queensland to 55% across northern Australia (see map). This means that cooler days are equally as likely as warmer days.

probability of exceeding median maximum temperature - click on the map for a larger version of the map

Outlook confidence is related to how consistently the Pacific and Indian Oceans affect north Australian temperatures. During the June to August period, history shows the effect on maximum temperatures to be consistent to moderately consistent over most of northern Australia (see background information).

probability of exceeding median minimum temperature - click on the map for a larger version of the map

The average minimum temperature for the start of the dry season (June to August) is favoured to be below the long-term median minimum temperature across all of the Northern Territory and western parts of Queensland. In these areas the chances of warmer nights is less than 40%, with probabilities of below 30% in the Victoria River and Tanami regions of the Northern Territory. This means that for every ten years with ocean patterns like to the ones currently being observed, six to eight dry seasons would be expected to be cooler than average, with only two to four being warmer.

History shows the oceans' effect on minimum temperatures during the June to August period to be moderately consistent over most of northern Australia.

 

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 23rd June 2011

Corresponding rainfall outlook

Maximum temperature departures from average for February to April 2011 - base period 1961-1990

Minimum temperature departures from average for February to April 2011 - base period 1961-1990

 

Background Information

  • 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. 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 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)

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