Mixed outlook for June quarter maximum temperatures

The national outlook for maximum temperatures averaged over the June quarter (April to June) shows a mixed pattern of odds, with warmer conditions favoured in the west and parts of the south, while a cooler season is more likely through parts of the east.

The pattern of seasonal temperature odds across Australia is mostly a result of warm conditions in the Indian Ocean in February, with the Pacific Ocean having very little effect at all. The chance of exceeding the median maximum temperature for the April to June period is over 60% across WA, parts of the northern NT and far north Queensland, and in a band from western SA to western Victoria. The strongest shifts in the odds are in WA where the chances of a warmer than normal season climb to over 80% in the central-west of the State. Odds in southeast Queensland and northeast NSW are shifted in the opposite sense: a higher than normal seasonal average has a 30 to 40% chance of occurring, meaning there's a 60 to 70% likelihood of a cooler than normal season. This is consistent with the rainfall outlook which favours a wetter three months in the same area. Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian temperatures. During the June quarter, history shows this effect on maximum temperatures to be moderately consistent over large parts of the country, especially in the north and west (see background information). The outlook for June quarter minimum temperatures also shows a pattern of strongly contrasting probabilities, with a 60 to 80% chance of a lower than normal seasonal average (i.e. 20 to 40% chance of warmer conditions as on map) across southeastern Australia. The odds swing the other way across Queensland, northern NSW, parts of the northeast NT and western to central WA where the chances are between 60 and 80% for the average minimum temperature to exceed the median. History shows the oceans' effect on minimum temperatures in the April to June period to be moderately consistent over large parts of the country.

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Regional versions of this media release are available: | Northern Aust | Southeastern Aust | WA |

Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:

THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24^th April 2009

Corresponding rainfall outlook

Maximum temperature departures from average for December 2008 to February 2009 - base period 1961-1990

Minimum temperature departures from average for December 2008 to February 2009 - 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 or from SILO (www.bom.gov.au/silo/products/SClimate.shtml).

• 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 23 El Niño events since 1900 are summarized on the Bureau's web site (www.bom.gov.au/climate/enso/).