THE BUREAU of Meteorology says an El Niño weather event, which correlates with drier than average conditions in Australia, is now unlikely this spring.
However, at present, a sustained ridge of high pressure, is playing a part in stopping rain delivering low pressure systems hitting is driving conditions and shows no immediate signs of abating.
The block of high pressure is remarkable.
It is some five hectopascals higher than average for June in southern Australia.
The Bureau of Meteorology predicted the likelihood of a dry winter in southern regions in its latest three month rainfall forecasts, issued in late May, where it rated some parts of Western Australia’s cropping belt just a 20 per cent chance of exceeding median rainfall.
So far, the prognosis has been accurate, with virtually all of Western Australia, South Australia and Victoria experiencing lower than average June rainfall.
Catherine Ganter, senior climatologist with the Bureau of Meteorology, said there had been an easing of warming in the eastern tropical Pacific Ocean.
“In the atmosphere, the trade winds and Southern Oscillation Index are well within the neutral range and sea surface temperatures near Peru cooled during March and April,” Ms Ganter said.
She said forecasting models used by the Bureau of Meteorology had also eased off their predictions.
“In April, seven out of the eight models were suggesting a possible El Niño, that is back to zero now,” Ms Ganter said.
Focus now turns to the other key driver of rainfall in the Australian spring, the Indian Ocean Dipole (IOD).
Ms Ganter said the news there was mixed.
“Three out of the six models suggest an IOD positive event, consistent with drier conditions in Australia, could develop.
“That figure is down from five in April, but it is still obviously a possibility.”
In terms of the current weather patterns, which have seen areas in the northern Western Australia wheatbelt and South Australia’s Eyre Peninsula in particular not receive sufficient rain to germinate crops, Ms Ganter said a positive Southern Annular Mode (SAM) had played a role.
“This is creating the strong high pressure systems which mean there is a blocking pattern that pushes those low pressure systems that bring rain to the south,” Ms Ganter said.
Much of southern Australia’s winter rainfall comes from constant cold fronts pushing through, with frequent, relatively low volume bands of rain.
Higher totals, associated with tropical moisture, are more likely in the spring.
“We will still get some frontal systems hitting southern areas but they just might not be so frequent.”