The coldest day (max) I've ever experienced was 10 degrees in September 1997. I remember it because I was riding in short nicks and one short sleeve jersey. It was bloody cold, and it wasn't really a ride to be enjoyed.

Parts of Sydney can get below freezing overnight on a frequent basis, like the Blue Mountains in the west. Riding over Berowra is very cold in the middle of winter because the wind from the snowfields blasts across the top of the plateau. Near freezing, but windchill factor makes it brass monkeys.

Other than that the place is positively tropical. Well temperate, at least.