National temperature outlook
Issued 22 May 2013
There’s a greater than 60% chance of this year’s winter maximum temperature exceeding the long-term median maximum temperature over the tropical north coastline, the southern and western coastline of WA, southern Victoria, and Tasmania (see map above). Probabilities exceed 80% over Tasmania, and the far southwest of WA. 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 southeast WA, the southern NT, most of SA, southwest Queensland and most of 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 in excess of 60% over the tropical north and southern Australia, extending up through western WA. Probabilities exceed 80% over the far southwest of WA, the south coast of Victoria and Tasmania.
Over the rest of the country, the chances of warmer or cooler night-time temperatures are roughly equal.
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 sometime 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.
How accurate is the outlook?
Outlook confidence is related to how consistently the oceans and broadscale climate affect Australian temperatures. During winter, model accuracy shows the outlook for maximum temperatures to be moderately consistent over northern and eastern Australia. Elsewhere, the effect is only weakly to very weakly consistent.
The effect on minimum temperatures during this season is moderately consistent over most of the country, except for near the NSW-Queensland border, and the northern NT, where the effect is weakly consistent.