China is a large country, similar in size to the United States, so clearly weather patterns vary enormously across the country.  Harbin in the far northeast is subject to bitterly cold winters, while Hong Kong and the Southeast have a subtropical climate, hot and humid most of the year.  One generalization holds true for much of eastern China--summers are very hot, humid and rainy. 

 For current weather in China: http://weather.china.org.cn/english/i...

 The best climate in China is found in Yunnan Province.  Located in the South, but at high elevation, Yunnan Province is pleasant year round, but is very rainy in the summer months.  

In the South, Guilin is rainy from April through June with hot, steamy summers.  Winters can be quite cool. 

Hong Kong is rainy may through September.  Hot in summer and warm in winter. 

Shanghai is quite cool in winter, with hot and rainy weather during the summer. (You can call 12121, the system will tell you today and tomorrow's weather, it plays again and again, first time in Chinese, then in English)

Beijing has extreme weather ranges from hot summer months comparable to those in the south, with the most rain in June and July.  Winters are bitter, windy and cold.  Winters are also dry, with bright, sunny days and little snow. 

When travelling around China, it is important to be prepared for temperature variations.  For example, even during the hot summer months, temperatures may be cool at high elevations or at night.  Even during the cold winters of Beijing, it is possible to have relatively warm days. 

Since many of the tourist sights are mostly outdoors, it is important to be prepared to spend long periods of time outdoors.  In the north in winter, it is essential to have long underwear, hats, scarves, gloves, and a very warm coat.  Also, during the winter, some restaurants and indoor places will not be well heated so it is useful to be prepared to wear a jacket indoors if needed.  High-class hotels have good air conditioning and heat as needed.