Eastern Australia faces another round of rain and snow as La Niña watch declared

Australia Broadcast Center

2 days ago

Any hope of a premature end to winter is fading fast.
In fact, this weekend will bring some of the coldest weather of the season, as a two-pronged pulse of polar air sweeps well north.
After wintry precipitation this weekend across south-east states, including small hail and snow, further heavy rain will then develop along the New South Wales coast from Monday where this August is quickly becoming one of the wettest on record.
The prospects of cool and wet weather lingering into spring is also rising for central and eastern Australia — just weeks after a negative Indian Ocean Dipole (IOD) formed, the National Oceanic and Atmospheric Administration (NOAA) has now declared a La Niña watch for the coming months.
Twelve months ago, Australia's capitals were baking in unseasonable summer-like temperatures, including monthly highs of 33 degrees Celsius in Brisbane and 30C in Sydney, and 25C in Adelaide.
Since 1910, August 2024 was nationally the warmest on record, following the third warmest in 2023. However, there will be no repeat of late winter warmth this year.
A cold front swept onto the southern coastline on Friday, introducing polar air from the Southern Ocean, and with a second front trailing on Sunday, south-east states can expect an extended spell of temperatures as much as five below average.
For today, isolated to scattered showers will impact southern South Australia, much of Victoria, and parts of NSW and Tasmania.
The presence of a sub-Antarctic air mass will also lead to pockets of small hail and snow to low levels, although a lack of moisture will limit falls in non-alpine regions to just a centimetre or two.
Saturday's lowest snow levels：
So where could snowfalls arrive today?
Dozens of non-alpine towns along the ranges may see a dusting, including on the higher hills around Trentham and Mount Macedon in Victoria, along with Bombala, Nimmitabel, Cooma, Jindabyne and Adaminaby in southern NSW.
A few flakes are also possible this afternoon and tonight on the higher NSW Central Ranges and the Barrington Tops.
The second pulse of polar air on Sunday will take a more western path over SA and western Victoria, and bring another round of showers and small hail.
The trajectory of the coldest air over SA could lead to a rare light snowfall in the state, most likely on the higher Mount Lofty Ranges and southern Flinders Ranges.
For Adelaide, Sunday is likely to be the coldest August day in five years with a maximum struggling to only 13C.
Snow could then redevelop along the NSW ranges from Monday as the polar air tracks east, possibly including another snowfall on the Northern Tablelands, and the first settling snow of the year around the Blue Mountains.
While the east coast will be spared a third consecutive weekend washout, as the polar air tracks east it will combine with moist onshore winds off the Tasman Sea to generate another week of rain.
Model guidance on the amount of rain and location of the heaviest falls is currently variable, however the general consensus is between about 50 and 100 millimetres from about Brisbane to the Illawarra, although for now, heavy rain extending north of the NSW border is somewhat uncertain.
For Sydney, where this August has already been the wettest in 27 years, another 100mm would make it the fourth wettest August since records began in 1859.
The notable increase in recent rain across parts of Australia is partly the result of a wet phase of the Indian Ocean forming this winter, called a negative IOD.
Once formed an IOD event normally lasts until December, but spring rain from this year's episode could be enhanced by the formation of a corresponding La Niña in the Pacific Ocean.
The Bureau Of Meteorology no longer issues watches or alerts for climate drivers, however a watch was declared by NOAA this week after surveying a range of modelling through the coming months.
"Based on this guidance and recent changes in the tropical Pacific, the forecast team narrowly favours La Niña thresholds being reached in three overlapping, three-month seasons," it stated in their monthly diagnostic report.
However, even if La Niña thresholds are met this year, the event is looking short and weak, meaning in isolation the episode is unlikely to cause widespread flooding across Australia.
But while La Niña's influence might remain minor, when combined with the wet signal from the Indian Ocean along with warm local waters surrounding Australia, the scales are still strongly tipped to indicate frequent rain this spring.