While large parts of the country have been baking or battling bushfire, Thredbo in New South Wales recorded Australia's lowest maximum summer temperature on record.

Key points: On Monday the temperature only got up to -1C at Thredbo, the coldest summer day on record.

On Monday the temperature only got up to -1C at Thredbo, the coldest summer day on record. The cold patch brought 20-30cm of snow to alpine parts.

The cold patch brought 20-30cm of snow to alpine parts. Meanwhile other parts of the country recorded their highest-ever temperatures.

On Monday, the second day of summer, the temperature only reached -1 degrees Celsius at the Thredbo weather station, the coldest maximum temperature recorded anywhere in Australia during summer.

The previous record was -0.8C, recorded at Mount Buller in Victoria on Christmas Day 2006.

The cold patch this week resulted in big snowfalls for large parts of the alpine region and was the result of westerly winds bringing cold air from Antarctica.

Despite these temperature fluctuations, summer is still expected to scorch.

Blair Trewin, senior climatologist at the Bureau of Meteorology, confirmed that it was a summer as well as December record but pointed out there was more to it.

"In some ways it's not quite as impressive as it looks," Dr Trewin said.

"This is because before automatic weather stations were installed in the 1990s, manual observations at high mountain sites [like the top of Thredbo, Mount Hotham and Falls Creek] were very limited outside the ski season."

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He said at Thredbo they used to take observations at the top of the mountain in winter and in the village in summer.

Luckily they filed the data as separate stations so they could be differentiated, but most of the coldest mountain-top temperatures from summer before the '90s would not have been recorded.

"This means that effectively, you're really only looking at the coldest summer maximum of the post-1990 period," Dr Trewin said.

"We don't have any real information about high alpine summer temperatures before then."

That doesn't mean Monday wasn't a big deal.

Cabramurra, another station in the alpine region, with records going back to 1955, also broke its December and summer record for lowest maximum temperature.

The maximum temperature there on Monday was 2.8C.

The previous lowest summer maximum temperature was 2.9C, recorded on the December 2, 1969.

Parts of north-central Victoria, like Bendigo and Strathbogie, also recorded low maximum temperatures this week.

Why so cold?

There was a very strong south-westerly air flow bringing cold air from way down over the Southern Ocean up into south-eastern Australia.

"It's important to realise here that ocean temperature's seasonal cycle lags a couple of months behind air temperatures," Dr Trewin said.

Down over the Southern Ocean it is still slowly warming up after winter so we are much more likely to get these cold outbreaks in December than in March, even though it is technically autumn.

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According to Dr Trewin there is snowfall in the alpine regions at least once during most Decembers, but there was no denying this was a big one.

"We've seen reports of 20 to 30 centimetres at the alpine resorts," he said.

"In that sense it was a snowfall you might expect to see in December maybe once a decade or so."

This isn't the first time it has been cold in December

Dr Trewin said the Christmas day 2006 cold outbreak was a colder air mass than the one this week but passed through more quickly.

The minimum temperatures at the mountain sites were significantly lower than they were this time, but the daytime maximum temperatures were mostly a bit higher.

In that event in 2006 there was snowfall down to 500 metres around Melbourne. This time round it was more like 1000 meters, according to Dr Trewin.

This event has seen below average temperatures hang around Victoria, Tasmania and parts of SA for around a week but it is expected to warm up over the weekend.

Melbourne is forecast to get up to 37C this Monday.

No it doesn't negate climate change

Even in a warming climate, cold records can still occur, but they are much less frequent than heat records.

"Some work we did in 2010 found that in the 2000s in Australia, record highs were outnumbering record lows for Australia by a ratio of about 3:1 for maximum temperature and 5:1 for minimum temperature," Dr Trewin said.

The Southern Ocean hasn't only been lagging behind at the end of the seasons, it has also been warming up at a slower rate as the world around it warms.

"We perhaps see a few more of these type because the Southern Ocean hasn't warmed up as much as the land has. So you've still got the potential for cold air to come from the South. But, you know, record heat is certainly outstripping record cold. You see that globally as well."

Human induced climate change is about averages and not just one-off temperatures.

Several places in the northern tropics have had their highest temperatures on record in the past few days — Kowanyama in Cape York (41.9C), and Milingimbi (39.5C) in Arnhem land.

Perth airport is having its fourth day in a row over 38C, which equals the record long streak for days over 38 in December.

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