BOM forecasts very warm winter for Australia, with the jury out on rainfall
The long-range forecast shows a very warm winter, but rainfall predictions are far less certain (Supplied: Laurie Wilson)
Almost all of Australia, including the capital cities, is very likely to experience another "unusually warm" winter, according to the Bureau of Meteorology's (BOM) official winter outlook.
The June to August forecast shows large swathes of WA's south, Queensland, Victoria, NSW, Tasmania and southern South Australia are at least 3.5 to 4 times more likely to have both day-time and night-time temperatures in the top 20 per cent of all records.
It comes after 2023 saw Australia's warmest winter on record, with some meteorologists saying this year could be even warmer for some locations, though the BOM was cautious in making the same call.
For those hoping for a good snow season, it's a forecast that might sound concerning.
But BOM senior climatologist Simon Grainger said it wasn't out of the question.
A warm winter outlook doesn't mean there won't be individual days of frost, colder weather, or snow, but rather that the odds are favouring temperatures to be warmer than normal overall across the season.
Selwyn lifts stood still when a lack of snow delayed the NSW ski season last year. (Selwyn Snow Cam)
"Snowfall in south-east Australia is really determined by cold fronts, and weather systems that we can forecast in the short term," Dr Grainger said.
"So we can still get a single, big weather event that could make a significant difference to the overall snow season."
How wet will it be?
When it comes to rainfall – the more noticeable weather element for the season – the outlook for the season as a whole is less clear.
Parts of WA's mid-west, central Australia, and a small pocket of Queensland near Cairns are slightly favoured toward wetter than normal conditions this winter.
The rest of the country has a fifty-fifty chance of being above or below average, with several areas – particularly in the eastern states – showing a wide range of possible outcomes.
It's a forecast that probably doesn't offer much if you're wanting to know just how wet or dry it's going be.
But Dr Grainger said what the outlook was more clear on was that it's unlikely going to be extremely wet or dry anywhere in Australia.
"There's some slight increased chances of unusually wet in some parts of the interior of WA and some parts of WA, but not a very high chance," he said.
"And it's only really northern Australia showing any chance of unusually dry, but that's in the dry season so basically they get no rain anyway."
The picture also becomes a little clearer in June, with the month likely to be drier than normal for parts of eastern Australia, according to the outlook.
Parts of Canberra were covered in fog on a brisk autumn day last week. (Supplied: Ainsley Morthorpe )
Meanwhile, early forecasts for the July to September period see rain kicking up a notch for much of the country.
To come up with the odds for both temperature and rainfall, the BOM runs the same model 99 times, with slightly different conditions to capture a range of likely future scenarios.
WA and SA desperate for winter rainfall
The slim chance of a dry winter is particularly good news for WA farmers, who have faced some of their driest conditions on record over the last eight months.
Rainfall this week has begun to turn the situation around, but Department of Primary Industries and Regional Development senior research scientist Ian Foster said there was still a long way to go.
"There needs to be a fair bit of ongoing rain, not only to fill up soil profiles, but to also put water in some dams, that sort of thing," he said.
Good winter rain is needed for Northcliffe dairy farmer Wally Bettink, who has seen his dams run dry throughout summer and autumn (ABC News: Tyne Logan)
This autumn has been extremely dry in most southern parts of Australia, apart from NSW and south-east Queensland.
In south-west WA, residents of some towns ran out of water after nearly eight months without any rainfall to fill their tanks, while farmers in some of the most reliable rainfall areas of the state were looking at completely dry dams.
The drought has been compounded by heat in the west, with Perth's maximums on track to average just below 28 degrees Celsius this autumn, 3C above normal and easily the highest on record.
South Australia has also been facing dry conditions over recent months, with Adelaide recording even less rain in autumn than Perth, with just 16mm up to the 29th of May.
Why is the temperature outlook so much clearer than rainfall?
BOM's long-range outlook is based on a complex combination of the physics of the atmosphere, oceans, ice, and land, and incorporates climate change and natural climate drivers.
When strong climate drivers are in play, such as La Niña or El Niño, it can add confidence to the models for range.
But Dr Grainger said, in this case, there was no strong driver present to help make those rainfall forecasts more clear.
"Although there is some forecasts of [La Niña], and some chance of a positive Indian Ocean Dipole developing, it's all still currently neutral," he said.
"And so we're not seeing a very strong signal in the rainfall."
He said the links between global warming and temperature outcomes, however, were a lot more direct, which likely had boosted the confidence in the temperature outlook.
He said this included the sea surface temperatures.
There are signs La Niña could develop during the coming months, with several international climate models favouring its arrival by spring.
But that is not being factored into Australia's long-range rain and temperature outlooks, because the BOM's model, which is what the long-range outlook is based on, doesn't agree.
If La Niña develops during winter, it would greatly increase the chance of a wet spring and summer across most of Australia, when historically the climate driver has helped deliver some of the wettest seasons on record.