China’s climate is extremely diverse – the best time to visit will depend on where you're travelling to. The south is subtropical, with wet, humid summers (April–Sept), when temperatures can approach 40°C, and a typhoon season on the southeast coast between July and September. Though it is often still hot enough to swim in the sea in December, the short winters (Jan–March) can be surprisingly chilly.
Central China has brief, cold winters, with temperatures dipping below zero, and long, hot, humid summers: the three Yangzi cities – Chongqing, Wuhan and Nanjing – are proverbially referred to as China’s three “furnaces”. Rainfall here is high all year round. The Yellow River basin marks a rough boundary beyond which central heating is fitted as standard in buildings, helping to make the region’s harsh winters a little more tolerable. Winter temperatures in Beijing rarely rise above freezing from December to March, and biting winds off the Mongolian plains add a vicious wind-chill factor, yet summers can be well over 30°C. In Inner Mongolia and Dongbei, winters are at least clear and dry, but temperatures remain way below zero, while summers can be uncomfortably warm. Xinjiang gets fiercely hot in summer, though without the humidity of the rest of the country, and winters are as bitter as anywhere else in northern China. Tibet is ideal in midsummer, when its mountain plateaus are pleasantly warm and dry; in winter, however, temperatures in the capital, Lhasa, frequently fall below freezing.
Overall, the best time to visit China is spring or autumn, when the weather is at its most temperate.