Southeastern Australian temperature outlook

Warmer nights likely for much of southeast Australia

Text details of chance of warmer maximum and minimum temperatures

Summary

• Warmer than normal days are more likely in Tasmania and southern Victoria, with cooler days more likely across most of NSW and SA
• Warmer than normal nights are more likely across most of southeast Australia
• Climate influences include a warmer than normal eastern Indian Ocean, a neutral tropical Pacific, and warmer than average sea surface temperatures around much of the coastline
• Skill for maximum temperatures is moderate over most of southeast Australia, with lower skill in western SA, while minimum temperature skill is moderate over most of southeast Australia.

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• Wider Australian region
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Details

The chances that the winter maximum temperature will exceed the long-term median are greater than 60% in southern Victoria, with probabilities greater than 80% in Tasmania (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight years would be expected to be warmer than average over these areas, while about two to four years would be cooler.

Conversely, there is a 30 to 40% chance of warmer than normal days over the most of SA and NSW. In other words, there is a 60 to 70% chance of cooler than normal days over these areas.

The chance that the average minimum temperature for winter will exceed the long-term median minimum temperature is greater than 60% over most of southeast Australia, with the exception of northern SA, where the chances of a warmer or cooler winter are roughly equal.

Climate influences

The tropical Pacific has remained ENSO-neutral since mid-2012. Climate models surveyed by the Bureau of Meteorology suggest sea surface temperatures in the tropical Pacific Ocean are likely to sit on the cool side of neutral during winter 2013.

Four of five international models surveyed by the Bureau favour the development of a negative Indian Ocean Dipole (IOD) event 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.

Warmer than normal ocean surface temperatures currently surround much of the continent. Warmer ocean temperatures will tend to influence air temperatures in those areas closer to the coast.

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Outlook confidence

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.