Why do the temperatures vary so much in Australia?

Answer 1

Because it's so big.

It's not just wide but also long too so it covers many latitudes. Because of the angle of the sun different latitudes get more or less sun than others and are hotter or colder than others. Because Australia is long and covers many latitudes it has many temperature differences.

Then there is terrain. Australia is one big island (well the mainland anyway) so we have coastal weather, rain, wind and the like. But we also have a huge mountain range running down the edge of the east coast of Australia which catches a lot of the rain clouds so that they can't get inland. Therefore a lot of inland Australia is desert and with no rain to help grass and plants grow and no cloud cover to hold in the daytime heat the desert is scorching during the day and freezing at night (like most deserts). We also have high mountains which mean they get snow or at least very cold when low lying areas are not so cold just because of their altitude.

And I'm sure a meteorologist could explain it even better then me.

Answer 2

Australia is a vast country, so temperatures in the country range widely throughout the year, according to the locality and the season.

Summer daytime temperatures can range from just 17 degrees Celsius in Tasmania one day to 30 degrees the next. Victorian temperatures can be similarly low one day, yet they can just as easily experience weeks of a heatwave, in which daytime temperatures exceed 44 degrees. The deserts can be much hotter, of course, whilst in the far north, temperatures are not so much hot (34 degrees or so) as they are humid, making outside conditions very sticky and uncomfortable.

Probably one of the more temperate regions would be southeast Queensland, where temperatures are a little more consistent, averaging 28 to 33 degrees.

Similarly, Australia's average winter temperatures cannot be determined. Temperatures in winter range from below 0 degrees Celsius in the Australian Alps to a balmy maximum of 28 degrees Celsius or higher, often up to 32 degrees Celsius in Darwin, which is in the tropical north.