National temperature outlook
The chances of the July to September maximum temperature exceeding the long-term median maximum temperature are greater than 60% over the tropical north, the western WA coastline, and Tasmania (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight July to September periods would be expected to be warmer than average over these areas, while about two to four years would be cooler.
Conversely, there is a 20 to 40% chance of warmer than normal days over southern and central Queensland, most of NSW, northern and central Victoria, eastern SA, and an area near the WA-NT-SA border. In other words, there is a 60 to 80% chance of cooler than normal days over these areas.
The chance that the average minimum temperature for July to September will exceed the long-term median minimum temperature is in excess of 60% over the tropical north and southern Australia, extending up through western WA. Probabilities exceed 80% over the southwest of WA, much of the northern Australian coastline, and Tasmania.
Over the rest of the country, the chance of receiving warmer or cooler night-time temperatures is roughly equal (i.e., close to 50%).
A negative Indian Ocean Dipole (IOD) event is favoured to develop during winter-spring 2013. A negative IOD during winter-spring increases the chances of above normal rainfall, and thus cloud amount, over southern Australia. Increased cloudiness reduces sunshine hours, and hence daytime temperatures, over inland Australia.
The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model indicates an increased likelihood of La Niña forming during the next few months. This has increased the chance of above normal rainfall for northern and eastern Australia. However, international climate models surveyed by the Bureau of Meteorology suggest ENSO-neutral is the most likely outcome over the coming season, with the Bureau model showing stronger odds than most of a weak La Niña.
Warmer than normal sea surface temperatures currently surround much of western and southern Australia. Warmer sea surface temperatures will tend to influence air temperatures in those areas closer to the coast.
How accurate is the outlook?
Outlook accuracy is related to how consistently the oceans and broadscale climate affect Australian temperatures. During July to September, historical accuracy shows the outlook for maximum temperatures to be moderately to highly consistent over Australia.
The effect on minimum temperatures during this season is moderately consistent over eastern WA, most of the NT, eastern and central Queensland, eastern NSW and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent.
Contact us for more details
Outlook confidence (or accuracy) is measured by comparing how often the outlook favoured a particular category (for instance, when above median rainfall was more likely to occur than below median rainfall in a particular season), and that the more likely category was then subsequently observed. This measurement of skill is known as "Percent Consistent", and has been tested over the period from 1981 to 2010.
Strong consistency means that tests of the model on historical data show a strong relationship between the most likely outlook category (above/below median) and the verifying observation (above/below median). In areas with strong consistency, relatively high confidence can be placed in future outlook probabilities. Very weak consistency means the historical relationship, and therefore outlook confidence, is low. 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 chance.
A random forecast of above median rainfall will be correct about 50% of the time. For this reason, the green shading on the map shows areas where the model has greater than 50% accuracy only. In areas which are not coloured in green on the map, some caution should be taken when using the forecast, notably at times when there is not a strong driver of our climate (e.g., no El Niño or La Niña is present; for commentary on the state of the main climate drivers, please see our ENSO Wrap Up).
The skill at predicting seasonal maximum temperature is good for most of the year, with the lowest point during the winter seasons. Of the variables predicted (i.e. rainfall, and maximum and minimum temperature), maximum temperature performs best. The skill at predicting seasonal minimum temperature peaks during summer, late autumn and late spring. Skill is lowest during late summer and late winter.
What is normal for this period?
These maps show the median (or 50th percentile) maximum and minimum temperature for the given three months. The median temperatures are calculated from the 1981-2010 period.
The maps will differ from other median maps on the Bureau's website. This is because the dynamical model forecasts use an averaging period of 1981-2010. The quality of the dynamical model forecasts is in-part determined by the coverage and accuracy of the observations fed into it. Therefore, to be consistent from one year to the next, the Bureau has only run the model during the modern satellite era.
About the outlook
Using the outlook
The Bureau's rainfall seasonal climate outlooks are general statements about the likelihood of wetter or drier than average weather over a three-month period. The probabilities are generated from the Predictive Ocean Atmosphere Model for Australia (POAMA), the Bureau of Meteorology's dynamical climate model. It is important to note that they are not categorical predictions about future rainfall, and hence the success or failure of one individual outlook does not infer that the model has low skill. Skill is assessed over multiple runs of the model. Likewise, temperature outlooks give the likelihood or chance of exceeding the average maximum and minimum temperatures over the entire three-month outlook period. Information about whether individual weeks or months may be unusually hot or cold, is presently unavailable.
Probability outlooks should not be used as if they were categorical (yes/no) forecasts. These outlooks should be used as a tool in risk management and decision making. Greatest benefits accrue from long-term use, say over 10 years.
About the model
The seasonal climate outlooks are generated by the Predictive Climate Ocean Atmosphere Model for Australia (POAMA), a dynamical (physics based) climate model developed by the Bureau of Meteorology and CSIRO Marine and Atmospheric Research. This coupled atmosphere-ocean model is a state of the art seasonal forecast system. Read more about POAMA.
The POAMA model is undergoing continuous research and development. Advances in the science of seasonal prediction, improvements in the observations and how they are fed into the model, as well as increases in supercomputing power are just some of the ways the model's accuracy will increase over time.
El Niño and La Niña
Indian Ocean Dipole
Statistical model outlooks
The official dynamical outlooks supercede the statistical outlooks. Statistical outlook maps will continue to be available for a review period: