West China — cold, some snow
— Xi’an, Tibet, Xinjiang, Qinghai, Dunhuang…
In most areas, the temperature falls significantly, and it gets cold and snow starts to cover the ground. The average high is just above freezing in Urumqi, and it freezes nightly.
Xi'an gets cool days, and it usually stays above freezing at night. The days are still pleasant, and most days are clear. It rains infrequently, so this is good weather for touring and street shopping.
Clothing: What you should pack depends on the altitude. You'll need a coat everywhere. For Lhasa, wear sunglasses and dress in layers.