The region's run of exceptionally chilly mornings could become the coldest spell in more than three decades – and a return to milder conditions may be weeks away.
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The mercury dipped to 6 degrees on Monday morning, making it four days in a row of temperatures of 6.2 degrees or cooler.
That's the longest run of such days for Sydney in 17 years and Tuesday morning is a chance to make it five days - a stint not seen since 1983, Brett Dutschke, senior meteorologist with Weatherzone, said.
A strong cold front that moved through last Thursday brought in a large cool air mass that has not broken up.
"You have the coldness and it's dry, and that's what the stand-out has been," Mr Dutschke said.
Conditions have been particularly frosty inland, with Badgerys Creek dropping to below zero for the past three mornings and Richmond clocking up minus-1 during the past couple of days, Weatherzone said.
While strong, the recent cold front brought only a dusting of about five to 10 centimetres of snow to the alpine resorts.
Still, that snow has delivered some cheer to ski operators relying on the snow guns to keep runs open.
Much better prospects, though, are in store for late next weekend or early next week, when a much more powerful front moves across southern Australia.
"It looks like we'll have the strongest front of this season without a doubt," Mr Dutschke said. "And there could be stronger and more frequent fronts [to follow] than we had last winter and for several winters.
"We could have our coldest run of weather for a few years for a large area of south-eastern Australia," he said.
"It's probably colder than the run we're currently experiencing."
Cool pool
Global models are picking up some of that cool forecast.
A projection of global conditions based on international models made by the Canadian government's meteorological service suggests that, for the week from July 13, Australia can expect below-average temperatures. (See below.)
The blue regions - which cover Australia and few other parts of the planet - point to a probability temperatures will be below average for this time of year. Most of the rest of the globe, particularly the oceans, are likely to have above-average temperatures for the week of July 13-20, the Canadian service said.
Unlike the current spate of cold mornings followed by sparkling days in Sydney, the weather will start to turn cloudier with more chance of rain.
The city's below-average temperatures, in other words, may be more likely during the day than at night.
"It will start to affect day-time temperatures more than night-time temperatures because [next week's front] looks like it's probably got a lot of cloud and moisture attached to it," Mr Dutschke said.
Central and northern Australia, though, will most likely feel the cold most at night rather than during the day as the front pushes well inland.
"It looks like the jetstream's moving ... it's allowing polar air to travel further north," he said.
Given the El Nino event in the Pacific, moisture from the coming system will probably be less than in a neutral year, he said.
Even so, the snowfields should get some decent falls.
Either way, for Sydneysiders and many others, conditions are likely to remain cool for a while yet.
"It doesn't look like there's much chance of getting comfortably mild weather developing soon," Mr Dutschke said.
