After an exceptionally warm and dry autumn, it’s time to look ahead to see what’s in store for winter. The Bureau of Meteorology’s climate outlooks for winter, issued today, shows above-average temperatures and below-average rainfall are likely across southern Australia. While some of us will relish the prospect of a mild winter, the dry isn’t necessarily good news for everyone.
Warm lead-up to winter
Summer-like conditions continued into early autumn for much of southern Australia, including an exceptional heatwave in early April. Temperatures in autumn were warmer than average across much of the continent. New South Wales, South Australia, Western Australia and Victoria all experienced one of their warmest autumns since at least 1900. Overnight temperatures have also been warmer than average in most parts.
Very dry autumn for the southern mainland
For many southern areas autumn wasn’t just warm, it was also extremely dry. New South Wales, Victoria, southwest Western Australia and South Australia all had one of their driest autumns on record.
Many farmers in southern Australia look to the autumn break – the first significant rain event (25mm or more) after summer – to kick off the crop and pasture growing season. The autumn break arrived by mid-May across southern Victoria, eastern New South Wales and southwest coastal Western Australia. However, farmers in northwest Victoria, inland New South Wales, eastern South Australia and much of inland Western Australia didn’t receive an autumn break this year.
One of reasons for the warm and dry autumn in the south was higher than average pressure over southern Australia. The high pressure meant rain bearing cold fronts from the Southern Ocean couldn’t push up into southern Australia.
No strong influence from Pacific or Indian Ocean this winter
So, will this pattern of warm and dry continue? Two of the major drivers of Australia’s climate, the El Niño–Southern Oscillation (ENSO) in the Pacific Ocean, and its equivalent in the Indian Ocean, the Indian Ocean Dipole (IOD), were neutral during autumn, and are likely to remain so throughout winter.
Of the eight international climate models surveyed by the Bureau of Meteorology, seven predict winter will see ENSO-neutral sea surface temperatures in the central Pacific, with only one model forecasting a warming to El Niño levels by August.
Models also suggest the Indian Ocean Dipole (IOD) will remain neutral through winter. But there is quite a range of scenarios from the international modelling centres the Bureau assesses. One model is predicting a positive IOD over winter, one model predicting a negative IOD in spring, and the other four are neutral. Typically, when the ENSO and IOD are both neutral there is no strong shift in the outlook towards widespread wetter or drier conditions across most of Australia.
Explainer: El Niño and La Niña
However, when these major drivers are neutral, other factors can have a greater influence on Australian rainfall and temperature patterns. For instance, forecast warmer-than-usual temperatures in the Tasman Sea and the associated lower-than-normal air pressure this winter is likely to contribute to a weakening of westerly winds over southern Australia that would normally draw cold fronts up from the Southern Ocean.
So, what’s the outlook for winter?
As a result of the weakened westerly winds, below-average winter rainfall is likely for western parts of Western Australia, and for most of New South Wales extending across the border into southern Queensland and northern Victoria. For most other parts, the outlook is neutral, meaning roughly equal chances of above- or below-average rainfall.
The outlook for June is looking particularly dry across most of the southern mainland.
The likely reduction in cold fronts, and clearer skies over much of the continent means warmer-than-average temperatures are favoured across southern Australia, with the strongest likelihood (about 80%) in the southeast.
The model suggests there is also an above-normal likelihood of winter “mildwaves” – periods of very mild weather – along Australia’s southeast coast.
So, what does this all mean? For farmers and those working in the agricultural sectors, the warmer temperatures mean soils will stay warm longer. This is likely to keep the crop and pasture growing window open a little longer before the cold of winter. Dry conditions are likely to mean a slow and possibly late start to the growing season, potentially pushing the crop harvest later into the warmer months of 2018, when heatwaves can become a problem.
What does this mean for the snow season?
For skiers, a later start to the season becomes more likely with a warm and dry June expected. On the other hand, neutral ENSO conditions typically bring snow cover that’s a little deeper than average by mid-season.
This is a contrast to strong El Niño or La Niña phases, which both typically mean less snow than usual, but for different reasons. El Niño phases mean less rainfall and warmer days during the snow season. La Niña years usually have more rain, but temperatures can be too high for snow to form.
This has happened more often in recent decades because of climate change. Historically, neutral years have had more consistent good snow depths than either El Niño or La Niña years, so late winter should be a good time to hit the slopes.
For more details on the long-range forecast for winter, visit our Climate Outlooks website and subscribe to Climate Outlooks to stay on top of what’s happening with the climate. A complete set of Climate Summaries covering May and autumn 2018 will be available on 1 June.
On the first day of spring, it’s time to take stock of the winter that was. It may have felt cold, but Australia’s winter had the highest average daytime temperatures on record. It was also the driest in 15 years.
Back at the start of winter the Bureau of Meteorology forecast a warm, dry season. That proved accurate, as winter has turned out both warmer and drier than average.
While we haven’t seen anything close to the weather extremes experienced in other parts of the world, including devastating rainfalls in Niger, the southern US and the Indian subcontinent all in the past week, we have seen a few interesting weather extremes over the past few months across Australia.
Drier weather than normal has led to warmer days and cooler nights, resulting in some extreme temperatures. These include night-time lows falling below -10℃ in the Victorian Alps and -8℃ in Canberra (the coldest nights for those locations since 1974 and 1971, respectively), alongside daytime highs of above 32℃ in Coffs Harbour and 30℃ on the Sunshine Coast.
During the early part of the winter the southern part of the country remained dry as record high pressure over the continent kept cold fronts at bay. Since then we’ve seen more wet weather for our southern capitals and some impressive snow totals for the ski fields, even if the snow was late to arrive.
Climate change and record warmth
Australia’s average daytime maximum temperatures were the highest on record for this winter, beating the previous record set in 2009 by 0.3℃. This means Australia has set new seasonal highs for maximum temperatures a remarkable ten times so far this century (across summer, autumn, winter and spring). The increased frequency of heat records in Australia has already been linked to climate change.
The record winter warmth is part of a long-term upward trend in Australian winter temperatures. This prompts the question: how much has human-caused climate change altered the likelihood of extremely warm winters in Australia?
I used a standard event attribution methodology to estimate the role of climate change in this event.
I took the same simulations that the Intergovernmental Panel on Climate Change (IPCC) uses in its assessments of the changing climate, and I put them into two sets: one that represents the climate of today (including the effects of greenhouse gas emissions) and one with simulations representing an alternative world that excludes our influences on the climate.
I used 14 climate models in total, giving me hundreds of years in each of my two groups to study Australian winter temperatures. I then compared the likelihood of record warm winter temperatures like 2017 in those different groups. You can find more details of my method here.
I found a stark difference in the chance of record warm winters across Australia between these two sets of model simulations. By my calculations there has been at least a 60-fold increase in the likelihood of a record warm winter that can be attributed to human-caused climate change. The human influence on the climate has increased Australia’s temperatures during the warmest winters by close to 1℃.
More winter warmth to come
Looking ahead, it’s likely we’re going to see more record warm winters, like we’ve seen this year, as the climate continues to warm.
Under the Paris Agreement, the world’s nations are aiming to limit global warming to below 2℃ above pre-industrial levels, with another more ambitious goal of 1.5℃ as well. These targets are designed to prevent the worst potential impacts of climate change. We are currently at around 1℃ of global warming.
Even if global warming is limited to either of these levels, we would see more winter warmth like 2017. In fact, under the 2℃ target, we would likely see these winters occurring in more than 50% of years. The record-setting heat of today would be roughly the average climate of a 2℃ warmed world.
While many people will have enjoyed the unusual winter warmth, it poses risks for the future. Many farmers are struggling with the lack of reliable rainfall, and bad bushfire conditions are forecast for the coming months. More winters like this in the future will not be welcomed by those who have to deal with the consequences.
Climate data provided by the Bureau of Meteorology. For more details about winter 2017, see the Bureau’s Climate Summaries.
You can find more details on the specific methods applied for this analysis here.