Hi, the temperature at the end of Dec in Yunnan is generally from 2-10C. It may be under zero at night. It is cold. You need to take some warm clothes. It seldom snow there. In fact, this places is suitable to visit all the year round. You can refer to Yunnan Tour Packages(https://www.travelchinaguide.com/tour/yunnan/) to plan your itinerary of travelling in these places. Whish you a wonderful time there!