If you've just switched on the TV to watch the cricket at a gloriously sun-bathed Gabba in Brisbane, where a maximum of 32 degrees is forecast, you might be surprised by what's brewing in the south of the country.

Melbourne (20ºC), Adelaide (21ºC) and Hobart (17ºC) are all expecting unusually cool maximum temperatures for this time of year. Meanwhile, snow is possible for the high country of New South Wales and Victoria on Friday afternoon or evening, in the first cold outbreak of the new year.

Snow could fall as low as 1500 metres in the Snowy Mountains of NSW and to 1400 metres in the Victorian Alps. Tasmania could also see snow above 1200 metres on Saturday.

Snow is not unusual in Tasmania or the Australian Alps in any month. There are no official statistics on the frequency of summer snowfalls, but anecdotally, you tend to get a few flakes two or three times each summer.

Here's a picture taken by this reporter on the Baw Baw plateau in southern Victoria last summer – several weeks before Gippsland was bathed in bushfire smoke.

Image: Baw Baw plateau, Vic, on December 3, 2019. Source: Anthony Sharwood

Cold fronts in southern Australia usually push a surge of heat ahead of them. For example on December 1 2020, it snowed down south on a day when Bourke in outback NSW reached 48ºC. And today, Penrith in western Sydney should reach 35ºC.

At other times, cold fronts play a very minor role in our summer weather patterns.

The weather this summer has been largely dominated by La Nina, with persistent cool, cloudy weather from the east which has brought heavy rain to many parts of eastern Australia. A pattern like this tends to push the Southern Ocean cold fronts further south so they don't impact Australia.

So what has changed in the last week?

The red hues in this multispectral satellite imagery highlight the cool, dry air mass crossing TAS, VIC and southern NSW. pic.twitter.com/Xpz8rUn5DM

— Andrew Miskelly (@andrewmiskelly) January 14, 2021

"During December, unusually high pressure over southern Australia limited the passage of cold fronts over our southern states," Weatherzone meteorologist Ben Domensino explains.

"However this week, we are seeing a stray pool of cold air from the Southern Ocean break through this high pressure ridge and pass over southeastern Australia.

"These cold air masses are more common during winter, although as we are seeing this week, snow can fall in Australia's alps at any time of year, even the middle of summer."

The good news about summer cold outbreaks is that they tend to be quite short-lived.

The snow that falls this evening in NSW and Victoria, and tomorrow in Tasmania, is serious news for alpine hikers and outdoors enthusiasts.

But by Sunday or Monday, things should ease, although the weather should remain cool for summer in much of southeast Australia until at least the middle of next week.