Five factors that favour drought relief during this winter's weather

Australia Broadcast Center

2 days ago

There are multiple signs a boost in rainfall this winter and spring will alleviate the record drought currently crippling southern Australia.
This optimistic outlook is due to the oceans and atmosphere around Australia transitioning into a state more conducive to precipitation.
There are five factors that point towards a significantly wetter winter and spring compared to last year across drought-affected regions — and only one influence that would favour the drought continuing at its current severity.
An extended spell of cold and showery weather will impact south-east states from Friday to Tuesday thanks to two cold fronts and low, the exact weather pattern that has been notably scarce over the past 18 months.
A typical winter front only brings a day or two of showers; however, a feature of the upcoming system is its longevity, which will allow rain totals to accumulate above 20 millimetres across most of southern and mountain Victoria, agricultural regions of South Australia and the NSW southern slopes.
For coastal regions of SA and Victoria, along with many parts of Tasmania, the winter storms should generate more than 50mm.
This upcoming soaking follows an initial first round of drought relief in late May when the best rain in months arrived across southern SA, south-west Victoria, and the NSW Riverina.
Remaining inland areas missed out on last week's rain, and while the next system will bring light falls, less than 10mm is likely across the northern Wimmera, Mallee, Murraylands, Riverlands and the western Riverina.
Along with farmers, a second group that will welcome the storm is ski resorts, which could gain 50 centimetres of fresh snow through the opening long weekend.
The general model consensus is that follow-up rain should arrive mid- to late next week as another cold front sweeps east across southern Australia.
The front is currently predicted to reach WA next Tuesday and then spread to south-east states by about Thursday, although being more than a week ahead, its strength and precipitation are uncertain.
By 10 days out, standard daily forecasts become unreliable — however, despite the limitations, medium-range forecasts do offer a guide to whether a certain week is likely to be wetter or drier than normal.
Current forecasts for the middle weeks of June show no strong swing favouring wetter or drier than normal conditions near our southern coastline — which at this time of year implies at a minimum some further rain is likely.
The exceptionally dry autumn in southern states this year was partly due to an almost total failure of Northwest Cloudbands (NWCBs).
Australia averages 36 NWCB days per year, and they are responsible for the vast majority of cool-season rainfall in many inland regions.
The first NWCB in 2025 did not arrive until late May, and while it delivered record falls to parts of the NT and Kimberley, unfortunately its path was well north of SA and Victoria.
The absence of NWCBs can be partly traced back to the waters off the WA coast — essentially, they are too warm to provide the required temperature variation between the tropics and mid-latitudes.
And while the marine heatwave off the west coast is showing little sign of waning, waters have recently also warmed south of Indonesia, which is increasing the thermal gradient off Australia's north-west coast — a pattern more encouraging for the development of NWCBs.
Another reason NWCBs may become more frequent through the remainder of the year is the possibility of a negative Indian Ocean Dipole (IOD).
A negative IOD is the Indian Ocean's version of La Niña and has a similar influence on rainfall by shifting cloud formation towards Australia.
The last three negative IOD years, 2016, 2021 and 2022, all produced very wet winters and springs across many parts of the country — and the majority of global models are forecasting a negative IOD will develop during the coming months.
While seasonal outlooks can be notoriously unreliable in early winter, there are already signs the transition to a negative IOD may have commenced.
The key monitoring zones for the phase of the IOD are shown below in the black boxes, and during the past week sea temperatures have fallen off the Horn of Africa and warmed off the coast of Java.
If this trend were to continue for another few weeks, negative IOD thresholds may be reached this winter.
The final reason for optimism is seasonal forecasts for the upcoming months range from either near normal to above average rain for southern Australia.
The Bureau of Meteorology's modelling in particular shows a strong swing favouring above-median rainfall during the next few months across the inland region — displaying up to an 80 per cent probability for northern parts of SA.
Even if rainfall is above average for several months, the significant deficits of 100 to 500mm that have accumulated in southern Australia through the past 18 months are unlikely to be removed until multiple seasons of above-average rain are recorded.
It's also worth considering the potential that rainfall remains well below average, an outcome plausible if a negative IOD and NWCBs do not materialise.
Another factor that reduces the prospects of rainfall this year is climate change — there has been a declining number of fronts observed over our latitudes in recent decades due to an expansion of tropical circulations into the mid-latitudes.
Although the long-term trend indicates droughts in southern Australia will therefore become more frequent and severe, in the shorter term, the balance of probabilities still suggests drought relief is ahead.