I'm intending to go to the tibetian areas in west sichuan and yunnan during december.

Of course. Both areas are accessible in Dec. They cover a large area with many attractions, so you'd better make a good plan in advance. In addition, if there is heavy snow, some roads with bad condtions may be closed. It is also suggested to check ahead the weather forecast in case. At last, it can be cold in the areas, so I suggest you prepare some thermal clothing.

thank you very much for your answer!