Hi Carol, Du Fu Thatched Cottage, Wuhou Temple,Jinli Old Street, Ermei mountain and Jiuzhai valley area are all the can't missing.
December is cold during the daytime and very cold at night. The average high temperature is around 11 °C (52 °F ) and the average low temperature is 5 °C. December is the driest month in Chengdu, but not as dry as most other Chinese cities in winter. It may snow in the mountains, and the sun rarely shines. Bring warm clothing like a thick sweater and an overcoat if you plan to be outside for a long time. Also wear a hat, gloves, and a scarf to avoid catching a cold.
Many tourist attractions are not at their best during December, but you can go to Xiling Snow Hill and Longchi Forest Park to see the beautiful snowy scenery.Whitney Liao replied on 2012-11-06
13 days are two much for Chengdu and JIuzhaigou tour, 10 will be enough. The place we recommend are:Du Fu Thatched Cottage, Panda Breeding and Research Center, Wu Hou Temple , Dujiangyan Irrigation Project, The front gate of Mt. Qingcheng, Leshan Giant Buddha and Monastery of Ten Thousand Years(on Emei Mountain).
For Jiuzhai valley, the main attractions are Jiuzhai valley park and Huanglong Park. 3 nights stay are enough.
I‘ll send you an email and quote for you by email.Leon Long replied on 2012-08-04