Will farmers get a break when the current La Nina subsides?
The Bureau of Meterology's cautious answer is "maybe". Neutral conditions are forecast to prevail for a while after La Nina takes her last bow sometime in late summer or autumn—except that no-one is quite sure what "neutral" conditions look like anymore.
And La Nina may hold more havoc up her damp sleeve before she exits the climatic stage.
The Bureau of Meterology (BoM) continues to run with its prediction of an above-average season for tropical cyclones, thanks to La Nina's strength and the current warmth of the Coral and Arafura seas.
Only one cyclone has made landfall to date, but Andrew Watkins, manager of BoM's Climate Prediction Services, says northern cyclone activity tends to peak in February-March.
La Nina is expected to persist at least until then, with some models putting her demise well into autumn. Normally the event begans to falter in December-January.
In a reverse of the El Nino phenomenon, conditions for La Nina occur when Australia's northern seas are warm, and the eastern Pacific is cool, creating a convection current that streams moist Pacific air over eastern Australia.
La Nina's persistence can be gauged by sub-surface temperatures in the eastern Pacific Ocean, Dr Watkins said. Unlike surface temperatures, which can change relatively quickly, sub-surface temperatures act like a climatic flywheel. Slow to shift to a new temperature, they are also slow to shift back.
Queensland may have had enough of La Nina, but the conditions that generated the event are also contributing to a mirror cycle in the Indian Ocean that has streamed moist air from north-western Australia down to the south-east.
Without that rainfall—albeit often badly timed for farmers—south-eastern Australia might be enduring an extension of its long-running drought, Dr Watkins said.
While the Indian and Pacific oceans have been contributing moisture to the Australian landmass, the all-important Southern Annular Mode (SAM) is in retreat.
SAM describes how the fronts blown around Antarctica shift north and south with the seasons. In winter, SAM moves further north, so the fronts typically contribute winter rainfall to southern Australia's Mediterranean climate. In summer, SAM moves south, and the rain falls out to sea.
SAM has been in an extended positive phase, and its rain-bearing fronts are not making landfall.
For south-west Western Australia, this has contributed to a record-breaking dry spell. South-eastern Australia has been watered largely by events that began in the Indian Ocean.
What is unclear is whether SAM will return to contributing good winter rainfall to southern Australia after La Nina breaks down, when the BoM's models forecast a spell of neutral conditions.
As Dr Watkins explained, "neutral" conditions—when climate isn't pushing strongly toward a dry or wet phase—doesn't necessarily mean "just right" for farmers, especially in southern Australia.
Modelling climate under global warming shows that higher ocean temperatures take SAM further south, so winter fronts make less landfall.
It remains to be determined whether the dryness of southern Australia over the past decade or so is an early harbinger of this phenomenon, or just a phase. Dr Watkins believes that a new "normal" is in the making.
"For much of southern and eastern Australia, the average has become slightly less rain in autumn and winter—we saw that in 2010 for much of the Murray-Darling Basin. It's a little harder to put your finger on 'average' these days."
The BoM is pretty happy with its forecasting leading up to the current La Nina, which it began calling as a strong possibility in June 2010.
In August, the BoM's seasonal outlook for September-November was relatively mild, with only modest chances of exceeding average rainfall in eastern Australia and south-west.
A month later, in its October-December forecast, BoM was predicting a very different picture. It suggested that Central Queensland had a 75 per cent chance of above-average rainfall—a forecast that led to briefings with the Queensland Government on flood preparedness.
BoM's January-March outlook suggests a reprieve from rain for most of Queensland, except the extreme south-east.
This area, with northern and eastern NSW, and the Pilbara region of WA, are predicted to have a 65-70 per cent chance of above-average rainfall as La Nina presumably enters its final phase.
* The Victorian DPI has put together some concise animations of the "climate dogs" that drive weather in Australia's south-east. The clips can be viewed here.
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