How cold is it in December (when it's Australia's summer holiday)? When else is the best time?
The weather in Yunnan Provence is about as wide ranging as the environments itself - so it really depends on which part you are planning on visiting. The souther part of the Provence that boarder Laos and Myanmar is pretty much sub-tropical, but further north around Lijiang there's a ski resort - so it's pretty cold most of the year. In general the further south you travel the warmer and wetter it gets.
My advice from experience - stay away from the mid and souther regions between May and October when things are at their wettest. Best time of year is probably around March/April/May - on the shoulder of the dry/ wet season. However, if you're planning on going during the Aussie Summer (December) then be prepared for temperatures from about 0 - 15 degrees Celsius in Kumning. remember, it's northern hemisphere so rug up as it's the middle of winter. about 9 years ago
I suggest not to go during summer (Aug - Oct) because it's wet season over there and it can get quite dangerous as you need to catch a bus or share a car to get to a lot of destinations.
It depends on which part of Yunnan you are going to visit, i went to Lijiang in December for Xmas and a long sleeve tee and a thich jacket will keep me warm, but if you are going up to the snowy mountain, put a jumper under your jacket will be fine.
Kunming is always quite warm and that's why it was named "Spring City"... about 9 years ago
The spring city of Kunming has beautiful weather almost all year. It just cold (even snow) for a month in Jan/Feb and its hot for another month in mid summer. The rest of the year is 20 - 25 every day. I wouldn't worry too much about the 'wet", it tends to just be a storm that passes through. (There has been a big drought there lately too.)
The rest of Yunnan rannges from tropical say in Xishuangbana near Myanmar and colder in the Dali and Lijiang regions. It a lovely place to live and travel. Don't forget the rice terraces down south in Yuanyang. This was an inspiring place...... almost 9 years ago