National Seasonal Temperature Outlook: probabilities for May to July 2013, issued 23rd April 2013

Warmer days favoured for southern and western parts of Australia; cool for parts of the east and interior

The national outlook averaged over May to July 2013 shows that:

• warmer days are more likely over most of southern Australia
• cooler days are favoured over southeast Queensland and the border region between WA and southwest NT
• warmer nights are more likely over northeastern and southwestern Australia

This outlook is mostly a result of warmer than normal waters in the Indian Ocean, with near normal temperatures in the tropical Pacifc Ocean having minimal influence.

The chance that the May to July maximum temperature will exceed the long-term median maximum temperature is between 60% and 80% over southern and western WA, the southern half of SA, southern NSW and Tasmania; with the highest probabilities over Victoria, southeast SA and southeast Tasmania (see map above). Such odds mean that for every ten years with similar ocean patterns to those currently observed, about six to eight May to July periods would be expected to be warmer than average over these areas, while about two to four years would be cooler.

In contrast, there is 35 to 40% chance of warmer than normal days over southeast Queensland and the border region between WA and southwest NT. In other words, there is a 60 to 65% chance of cooler than normal days over these areas.

The chance that the average minimum temperature for May to July will exceed the long-term median minimum temperature is between 60 and 80% over southern and western WA, the Top End and eastern parts of the NT, Queensland and the northern half of NSW.

Over the rest of the country, the chances of warmer or cooler minimum temperatures are roughly equal (see map above).

Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian temperatures. During the May to July period, history shows the effect on maximum temperatures to be moderately consistent over the northern half of Australia, most of WA, the southern half of SA, southern NSW, Victoria and most of Tasmania. Elsewhere, the effect is only weakly to very weakly consistent (see background information).

The effect on minimum temperatures during this season is moderately consistent over most of WA, most of the NT and Queensland. Over southeastern Australia the effect is weakly to moderately consistent. Elsewhere, the effect is only weakly to very weakly consistent. Please exercise caution in areas of low skill.

 

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, Catherine Ganter on (03) 9669 4679, Elise Chandler on (03) 9669 4748.

 

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:

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 22^nd May 2013

Corresponding rainfall outlook

Maximum temperature departures from average for January to March 2013 - base period 1961-1990

Minimum temperature departures from average for January to March 2013 - 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. 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)