THE LATEST Bureau of Meteorology (BOM) climate forecasts suggest neutral climate drivers over the coming months, however looking further into spring the models throw up some interesting possibilities.
In its latest El Niño / Southern Oscillation (ENSO) outlook, the BOM said moving into September, two out of the eight models it used suggested there was a chance of an El Niño event occurring, consistent with drier than average conditions.
On the flip side, three out of six models are forecasting the potential for an Indian Ocean Dipole (IOD) negative event to form, which means wetter than average conditions in general.
So what does this mean for our weather?
CSIRO researcher James Risbey, who has conducted studies into what climate drivers influence different parts of the country, said it is more complex than simply weighing the two climate drivers against each other, important as they can be to weather throughout the nation.
“Firstly, neither driver is an actual determinant of above or below average rainfall in any particular area, they just alter the odds,” Dr Risbey said.
“Secondly there are an awful lot of other factors that influence the weather so it is simplistic to suggest one thing or another will be the sole influencer in weather patterns.”
However, Dr Risbey’s research has found certain factors are more important than others at certain times of the year in different parts of the nation.
“For instance, through Victoria in the winter blocking patterns and the southern annular mode (SAM) are important drivers of weather but by spring it is the IOD that is the major factor.”
Throughout the northern cropping belt, the ENSO readings are critical through winter and still important, although less so, through the spring, while Western Australia is dependent on frontal rain driven by the SAM through winter, when much of the rainfall for that state falls.
At present, farmers in Western Australia and areas closer to the coast in Victoria, SA and NSW are looking for blocking patterns to bring rain, while inland NSW and Queensland in particular are still being influenced by ENSO climate drivers.
BOM manager of climate prediction services Andrew Watkins said farmers should not get too caught up regarding ENSO and IOD forecasts at this time of year due to their poor accuracy.
“Climate model outlooks for ENSO and the IOD have lower accuracy during autumn than at other times of the year,” Dr Watkins said.
“Hence current model outlooks for these climate drivers should be viewed with some caution.”
Regarding the outlooks, Dr Watkins said he was not sure a true IOD negative was actually on the cards.
“At present it is the atmosphere directing the ocean temperatures, which is odd, normally it is the other way around.”
“The weather patterns are keeping cloud away, stopping convection, so that the ocean surface is warmer than normal because of the extra sunlight, not because of a warmer ocean with depth.”
He said this could mean a negative IOD would not drive the atmosphere like normal, because at present it is the atmosphere driving the IOD.
Dr Watkins said the odds were still on a neutral ENSO year, but added the grains industry needed to watch what was happening in terms of the SAM.
“Lower pressure in the mid-latitudes suppresses the westerly winds that normally bring cooler air and rainfall from the southern ocean, that is something that may play a bigger role in the coming months.”