China is vast - on the same day the north-south gap can exceed 30 degrees: Harbin at -20°C during Spring Festival while Sanya sits at 25°C. Check the 7-day forecast for your destination.
By season: spring (Mar-May) light jacket plus shirt, scarf against northern winds; summer (Jun-Aug) hot and humid - t-shirts, sunscreen, umbrella in the south; autumn (Sep-Nov) the most pleasant - long sleeves and light layers; winter (Dec-Feb) down jacket up north, light jacket down south (Guangzhou, Hainan).
North vs south: northern winters are "dry cold" with indoor heating above 20°C - take off the coat inside; southern (Shanghai, Hangzhou) damp cold is "magic attack" - equally cold indoors and out, so down jacket plus thermal layers win.
Plateau and mountains: above 3,000 m on the Tibetan Plateau or Yunnan, pack thick layers, sunscreen and sunglasses year-round; day-night swings exceed 15°C.
Practical: malls and metros run strong AC - carry a light layer in summer; hotels have AC or heating.
Rain: the southern plum-rain season (June-July) brings days of drizzle - pack a folding umbrella; during typhoon season (July-September) watch coastal flight changes.
