Located in the center of China and the center of Guanzhong Plain, Xian has a temperate and continetal monsoon climate. You can easily feel the change of four seasons but not so harsh. Hot and rainy summer, cold and dry winter. Xian's rainy season is from July to September, but from April to October, there are rains too. Spring (Mar. - May) and Autumn (Sept. - Nov.) are the best seasons to visit Xi'an because the climate are warm and comfortable.
Spring is from March till May. The temperature is fluctuate, but the warm sunshine and gentle breeze are always there for you to visit and do some outdoor activities in Xian.
Summer is from June to August. Xian is one of the major 'stove' cities in China for the scorching and hottest sunshine in summer. But it is humid too. There will be several days to rain during the hot days.
Autumn is from September to November. The weather becomes cool and cloudy from the hot and humid. In early autumn, there is a fair amount of precipitation. But in late autumn, it becomes dry and sunny again.
Winter is from December to February when the weather is cold, dry and foggy. Occasionally, there will be some snowfalls, but lasts short. You can ask to add a skiing to your tour of Xian.