It's been dubbed the "Antarctic vortex", a deep low to Australia's south that is likely to bring one of the most significant outbreaks of cold weather in 60 years to the southern and eastern regions of Australia.
And the chart below shows exactly what it looks like. The powerful surge of sub-Antarctic air that is now sweeping across southern Australia is bringing much-needed natural snowfalls to the main alpine resorts - just as many families return home from school holidays.
The cold front will bring some of the coldest weather in decades to Australia, Blair Trewin, a senior climatologist at the Bureau of Meteorology, said.
Early on Saturday, many of the state capitals were in single digits with Perth recording the lowest temperature - with its low almost 5 degrees below average for July.
Snow is likely to fall from Victoria all the way north along the ranges into southern Queensland, with many areas at elevations of only 600 metres above sea level likely to collect at least a dusting.
According to industry website Ski.com.au, Victorian resorts such as Mt Hotham and Falls Creek have already received seven to nine centimetres of snow on Friday, with Thredbo in NSW collecting 10 centimetres so far. (See the forecast map below for snowfall regions by Sunday morning.)
Guy Dixon, a meteorologist with Weatherzone, says Victorian resorts usually do better than NSW counterparts from a south-westerly flow such as the current burst, but most ski areas will get 20 to 40 centimetres from the storm.
The natural snow will help the resorts, which have relied heavily on man-made snow to keep ski runs open. Falls have been modest up to until early on Saturday, with Perisher and Hotham collecting a bit more than 10 centimetres faring best, according to Ski.com.au.
While few cold records are likely to be broken in coming days, the sheer size of the area affected may make it biggest event of its kind since 2000, Dr Trewin said. Over the past six decades, 1965, 1984 and 2000 were the stand-out cold events.
Melbourne won't get much relief for a week, as the frigid air mass settles in before another cold front moves across on Wednesday and Thursday next week. The city's maximums aren't expected to climb above 12 degrees until at least Thursday, with a top of just 11 predicted for Saturday.
Sydney will fare better, with a milder top of 19 forecast for Saturday, before temperatures drop to a maximum of just 14 degrees on Sunday, according to updated bureau forecasts. Maximums from Monday to Friday will be 15-17 with overnight temperatures of 7-8 degrees.
Strong wind gusts, though, will mean the accompanying wind chill will make conditions less bearable in Sydney on the coldest days. "It has the potential to feel more like 11 degrees at times," Mr Dixon said.
Hobart will also be deep in the chill zone with Wednesday currently forecast to be the coldest of the coming week, with a top of just 10 forecast.
'Warm wrap around'
While the ranges are likely to get some snow, just how long it will linger - and whether it gets blanketed by rain - remains rather uncertain.
Meteorologists say a "warm wrap around" may bring wet conditions as the cold front leaves behind a swirling low pressure system.
The right-hand chart below shows the path of relatively warm air from Sunday.
"A pool of cold air will shift northwards over NSW and relatively mild air will follow in its wake," Mr Dixon said
If that warmer air brings a lot of rain to the resorts, school children returning to their studies from the ski slopes may feel they didn't miss out on too much after all.
